I think Gambrel wrote somethings that aren’t exactly the true… With the LP you CAN use two knobs separately to control cutoff and resonance at the same time, by using the POT MAP function.
I won’t discuss the topic’s subject… I think both sound different enough to justify my purchase. 
Even if i can’t verbally describe the difference in the sound of the two Phattys I can certainly hear it!
I have been really digging the Sub Phatty — even more than I expected I would — my biggest complaint is that they should have used white for the lettering on the jacks like they did on the Taurus 3… so you don’t have to to dig out your iPhone flashlight every time you want to plug something in.
edit: Can’t seem to post the SoundCloud miniplayer version here ~ “SECOND LIFE of RILEY” is a track comparing the sound of the phattys with the sub controlling the slim’s arp feeding back into the sub :
SUB PHATTY panned left — SLIM PHATTY panned right
eurorack modular BOX dead zero centred. live one pass recording
—
from THE NINE LIVES OF RILEY
written & recorded May 2013
PETE DAKO © SOCAN 2013
https://soundcloud.com/misterpete/sets/the-nine-lives-of-riley
After reading this whole thread: can it be that the Sub Phatty actually has DCOs instead of VCOs?
How can the Sub Phatty control the oscillator beating otherwise?
NO. It cannot be. 
The Sub controls the oscillator beating by having very stable and well-calibrated VCOs, and by having a firmware function that calculates linear pitch-CV offset (for beat frequency) in additional to the usual exponential conversion (for musical pitch).
So torn on which one to pick up. Slim or Sub.
This is a great discussion, loving everyone’s input.
I own a Minitaur and its very limited, I’ve been sequencing it with mp mpc or oberkorn. I’d like to team it up with either the Slim or Sub both have pluses and are diferent…
I’d go for the SubP if I was you. You get that sweet vintage Moog sound and more knobs. 
I own them both and like each equally as good but for different reasons. I Would say figure out which one you will get the most use out of. The little phatty has more of a “warm analog” feel to it, the sub-phatty is more gritty and best suited for gritty baselines and screaming leads! Both equally as good but for different reasons! Good luck
Sub vs LP
The Sub oscillators are similar to the Minitaur in that they are very stable and yet can be quite warm and ‘analog’ sounding by making use of the same features that the Minitaur has…VCO Beat, OSC tuning and LFO modulation. Unlike the LP, the Sub has a wide range of pure tones that can be generated simply by adjusting the Oscillator/Noise Volume knobs and the multidrive knob…from clean and warm to dirty and cold. Oscillator volume balance is key to sound creation on the Sub. The under the hood features are very comprehensive and overall the Sub has a more flexible sound design engine then the LP. Workflow on the Sub is also faster and more efficient once you master the alternate functions and/or utilize the decent software plugin/standalone…the LP software is pretty poor and menu diving is tedious. The one thing I miss about the SP is the Overdrive which IMO is much more tasteful for sound processing then the Multidrive…however you can get a wider array of sounds using the Multidrive.
I own a Minitaur and traded my Slim Phatty for a Sub, so my point of view is based upon my personal use of these instruments. The Minitaur will complement either unit well. In fact you many appreciate the Minitaur more so, once you have a LP or Sub alongside it. The Taurus tone is unique. Overall I find the Sub to be a more useful product but if I had unlimited funds I could see adding an SP back into my setup for certain uses.