Here are the experiences I have had. All pedals tested with a Moog Subsequent 37.
AMT Japanese Girl Wah: Clips fairly easily, but it seems like most wah pedals do this unfortunately. It also has a fairly high resonance, which makes the wah very pronounced but the low end can get a little boomy or create weird feedback if running it into distortion. Also adds quite a bit of noise (not really audible at normal listening levels on headphones, but through an amp it is easy to hear.)
Boss CH-1 Super Chorus: I mostly like chorus on subtle settings, to add some slight detuning. This pedal didn't do that very well. If you like more extreme chorus it will do that, but the subtle settings were actually too subtle! It has separate dry and wet outputs, and the sound can improve using those, but that's nowhere near as nice as an actual stereo chorus. I have heard this used with better results on piano though, so depending on your set-up it may be worth a try; after all these things regularly sell for very cheap used.
Boss DM2W Waza Delay: I absolutely love this pedal. I have even used 2 of them set up in stereo to create stereo analog delay. They work beautifully with synth leads and the tone quality changes depending on the filter of the synth not to mention the delay time and mode. I prefer custom mode as it has much longer delay times and is still very dark. Standard mode almost sounds bit crushed, which is cool in its own right. I cranked the Moog's volume all the way up and did not hear any clipping. Highly recommended.
Boss RV-6 Reverb: Produces some long lush reverbs, but for me the basic sounds like room and hall seemed overly bright and digital sounding. The modulated mode was definitely the best. Very subtle modulation, but for ambient stuff it would be killer. The shimmer mode doesn't compare that well with some other pedals on the market, but it still gives a cool effect. If you want natural reverb though, I would pass on this one. I have not had any clipping issues with it other than if I turn all knobs up fully on one of the modes with a long decay and have the synth's volume all the way up, but if you keep the level of the synth and pedal balanced it works fine.
Boss TE-2 Tera Echo: This is a very unique pedal which combines delay, reverb, and weird filtered modulations together for some cool ambient textures. Excellent in stereo. The main problem with it is because it's so unique, you are pretty limited in the number of different sounds it will produce. There is a knob which makes the tone darker or brighter and that can help dial out some of the over-the-top sounds when they are not desired. It's very responsive to the type of sound used and the way it is being played. For example playing legato or staccato will affect the way the pedal reacts considerably. It also has a freeze function, which basically records 1 or 2 seconds of sound coming through the pedal and loops it. You can still play over it, until you let go of the pedal. Honestly I feel this was designed for synths and keyboards more than guitar, just be sure it's the sound you want.
Digitech Distortion Factory: If you want to make your keyboard sound like it's being played through a guitar amp (common for some electric pianos and clavs as well as synth leads,) this is super cool. It has 7 different models of classic distortion, overdrive and fuzz pedals, and you can also run those through the built-in cabinet simulator. It really made my Moog sound like a guitar. It also has a separate output for just the distortions if you don't want the cab simulation. Very nice set of tone-shaping controls so you can EQ the sound exactly how you want it. One major note, if using the output with the cab sim, when you bypass the pedal, the cab sim stays on. This was a deal breaker for me, as I need the cab sim but normally wouldn't want it on, just when the distortion is on. I don't care for distortions on their own without the amped tone to warm them up. But if that's not an issue, it's a great piece of gear and will really dirty up anything you feed into it.
Digitech Nautila: This is a chorus and flanger pedal. You can control the number of voices for each effect (maximum of 4 for flange, 8 for chorus) to get either classic or super lush tones. The flanger can even sound like a different flavor of chorus (more like a simple stereo detune) which I love. Great for turning a mono signal into a stereo one. It does clip fairly easily though, so you will need to turn the volume down while using it...but honestly it's almost worth it. It's not an analog-sounding pedal, but it will add a lot of depth and movement to patches.
Digitech Obscura Altered Delay: Lots of versatility with this one. I haven't had any clipping problems at normal volumes. The tape and analog modes are very nice. I don't really use the other 2 modes. Reverse kills the dry signal entirely so it has limited uses. Also, one important note is that while the pedal is in stereo, it cannot do any sort of stereo effects like ping pong.
Digitech Polara Reverberator: Much more natural-sounding to me than the Boss RV-6. Room and hall are my favorite modes, but modulate is also very useful. The shimmer mode is more subtle than most versions of this effect, which makes it more useful in my opinion. It also has a reverse verb, plate, and spring. Spring clips at almost any volume; all other modes don't seem to, though maybe they do and it's just not noticeable...
Electro-Harmonix Pitch Fork: Very nice pitch shifter if you do not need true harmonies (IE it can't harmonize in a defined key like some shifters can.) Fifths and octaves are probably the most useful settings. Naturally the shifted signal has a different tone to it but it is much better than others I've tried, tracking is perfect and there are no weird glitches. You can also use it for wammy effects, have 2 pitch shifted signals at once (one above and one below your dry signal,) and it even has a detune mode although unless you hook up an expression pedal the detune amount is fixed at an interval that is pretty far from the dry signal. For the most control, an expression pedal is recommended. It does add some noticeable hiss when turned on depending on the set-up you use; most of the time it has not been an issue for me.
Joyo British Sound and Joyo Orange Juice: These are amp simulators. Honestly not as much of a tone difference as I had been hoping for even with drive maxed. Amp sim pedals seem to be pretty useless on synths unless they have a cab simulator as well and preferably also have a higher amount of gain.
Joyo Nebulous Phaser: Super small phaser pedal which sounds great especially for $50! No noise that I have noticed, just nice smooth phasing. It will clip slightly at higher volumes but it doesn't seem to be too bad on this particular pedal. Well worth the price if you like smooth phasing that can go from very subtle to moderate.
Keeley Dyno My Roto: This pedal creates some awesome tones, BUT...I have to turn the synth's volume almost completely off for it not to distort. If you are using a re-amp box this won't be a problem; however I am not. Tri chorus mode is super lush and is great for thickening up basically anything. You have control over the depth, speed, and waveform, which can make the chorus very smooth or a bit more choppy and defined. There's also a rotary speaker effect and a flanger. The rotary effect was actually a lot more fun than I had anticipated, and I was able to get some very organ-like sounds created in no time. It also helps give some edge to more aggressive / guitar-like leads while keeping them from sounding too much like a distorted / amped guitar, as there is no distortion control on the pedal and a Leslie amp has a different character than a standard guitar amp anyway. In addition to that you can adjust the proximity of the mic from the cabinet to add some room ambience. The flanger sounds great though I rarely ever use a flanger. With the resonance turned up it was nearly impossible to get the pedal to stop distorting even at the super low volumes I already had it at. For the studio, this would be a great tool. For live, not so much unless you have a re-amp box.
TC Electronic Alter Ego V2: This is basically a vintage tape / analog delay modeler. It has various recreations of famous (and some not so famous) delay units. You can set the repeats to be in mono or stereo. In stereo, you get quarter notes on one side and dotted on the other. There's also a very easy to use looper included, as well as one toneprint slot for saving a custom designed sound (many are available on the TC site or you can create your own.) The possible downsides are that all presets have some sort of modulation, from subtle to extreme, and this is not adjustable on the pedal at all. For that you have to use the Toneprint editor, and then there is only one slot to save a custom sound, so if you're not happy with the stock mod settings your options will be limited. Secondly, it does click when turned on and off (more subtly than some pedals, but it is there.) It also clicks when you hold the switch down to go into tap tempo mode. Tap tempo is very easy to set however, assuming you don't need to adjust it in the middle of a song because it mutes your signal. You hold the switch down, then you tap in the tempo by playing a few notes at the speed you want. Also, when using the looper you are not able to use delay at the same time, and the volume will probably need to be adjusted as well as the volume knob effects the entire signal, not just the loop itself. Having said all of that, the Echorec and Space Echo modes are very nice, there's another super distorted tape echo on there (forget which one) which is also super cool, and the modulated reverse mode is fun to play with.
Now after saying all of that, I still have most of these and am planning on selling all except one Boss DM2W and making a smaller board with only a few pedals, ones specifically designed for line level. Already have a Source Audio Nemesis on the way and cannot wait!