The new Sequential Circuits Prophet 6 looks pretty amazing…seems to have a bit more analog flavor than the DSI line (I'm assuming because it doesn't have DCOs). Surely, someone on the forum has one by now, and they could share their opinion.
If I had the money, I'd have bought one already, even if I ended up returning it for a refund (like I did with two DSI synths––Mopho&Tetra). I just want to play with one for a few weeks and see if its worth the coin.
I can personally speak on the Nord and the Virus though, both incredible synths that I have experienced in depth.
Nords I've owned: Lead, Lead2x, Electro, and Electro 2 Rack. I currently own the Electro 4D, and absolutely love it. I find that approaching it like a synthesist (instead of a traditional keyboardist) can render some incredibly unique sounds. I've just recently become obsessed with making otherworldly sounds with various synths, then loading them onto the Electro as a wav. file and playing them across the keyboard through various effects (both onboard and pedals). Endless fun. So much fun in fact, that I'm starting to really lust over the Nord Wave.
As for the Virus. I've owned: TI1 (61key), TI2 (61key), TI Polar, and TI2 rack. I currently own the TI Snow. That's right, I kept getting smaller and smaller with my Virus-selection until I reached their tiniest model.

These can be incredible synths, but honestly I had serious problems with both of the 61-keyboards (ghost-notes, stuck-noted, random artifacts). I really loved the Polar, and had very little problems with it other than minor MIDI issues. The rack was also great with no significant issues. The Snow ended up being perfect for me because I use my Virus for a very specific sound (mainly soft pads/strings, and spacey ambience). The Sub37 and Electro are the main boards in my rig so I never tweak the Virus in a live setting, therefore I don't mind the lack of knobs. The other difference is, the Snow can only layer up to 4 parts, whereas the TI's can layer up to 16…which seems really cool in theory, but after having TI's for a couple of years I discovered that I very rarely made sounds using more than 4 layers.
Other synths I've owned and not cared for… Korgs. Nothing against the old analog stuff, or the new I suppose (other than the cheap flimsy built-quality, ha). But, I pretty much went through their whole digital line in the early oughts. MicroKorg, R3, Radias, ESX1, EMX1, KP2, KP3, and Kaossilator. Eventually, I ended up selling every single one them because I never liked the sound enough, the tone never fully satisfied.
Which brings me to what I consider the bottom of the barrel (and I apologize if this offends anyone

), most of the "modern" digital Rolands and Yamahas just sound like shite to me…(I swear I've heard better plug-ins). I haven't had a chance to check out the Airia system in person yet, so I can't speak for it. But, it almost seems like you have to go back in time to get a cool-sounding Roland or Yamaha.
I'm also pretty sure Waldorfs sound amazing, and I'll probably buy one someday just to find out for certain.
Well, I hope my wordy rambling provided some help in your search for a great poly. Good Luck.