I purchased a PPS M2 and never have shot or held the classic so I can't compare. I can say that the ergonomics of the M2 feels good in my hand and the felt recoil is not at all jarring as some guns can be. If you buy new, read up on the site here about some of the break-in characteristics of the PPS so you can be better prepared. Once broken in, mine appears to be settling in to being a really nice gun.
I own both an I definitely prefer the M2. I am much more comfortable with the mag release on the M2 and the ergos are a huge plus. 7 or 8 round mags are a must. If I could carry in my state the PPS M2 would be a serious contender for me.
Had the M1 40 cal. for about a 18 months, got it from Buds for 359.00 new. Great gun. But I did not like the paddle release because of muscle memory. The one big thing that really turned me off was the backstrap release. Went to load it one day and hit that lever at the bottom of the mag well and it popped out just enough to lock up the whole gun. Not using a roll pin to lock it in place was a really bad design flaw, IMO. Just bought my second PPS M2 LE. Fits my hands better than any other pistol I've ever owned. The xds, g43 and shield were all nice, but the PPS just fits better.
I have both in 9mm. Bought the M1 right when the M2 came out, when they first started with the deep discounts on the M1s. Loved it right out of the box, especially when I put a Talon Grip tape on it.
Then I switched my primary "large gun" carry from HK back to SIG and that meant button mag release. For the sake of continuity I decided to get an PPS M2. Loved it right out of the box. Shot a couple thousand rounds through it over the past 2+ years while the Classic sat in my safe.
Then this winter I got to thinking about how nice the Classic had felt, and I pulled it out. Damn! That gun felt great in my hand. I bought a new Talon grip (the other was getting a little ratty), took it to the range, and fell in love all over again. Decided to start carrying it again. I've carried it for the past 8 months while the M2 sits in the safe.
In the end, for me the ergos of the Classic feel better than those of the M2. Completely counterintuitive to what I expected before handling the M2, AND to what I thought I felt at first when the M2 was new.
For me: with factory grip, VERY slight edge in grip ergos for the M2. With Talon wrap on both, I prefer the Classic by a good margin.
I have an m1. Bought it before the m2 was released and before the price drop. I like the paddle and the more flat profile.
Spare part on hand RSA backstrap and extractor.
Also two of each 6 7 8 round magazines.
I have the Classic in .40 and an M2 in 9mm. I like em both but carry the .40 Classic every day.
I don't worry too much about muscle memory, I think training your subconscious is more important and that can be done much more quickly than developing "muscle memory". Plus it can be reversed through similar repetition.
Either model is a fine choice. I'm not thrilled w the M1's backstrap "safety", but it's never been an issue. I also think the M2's trigger holds a slight edge.
So why do I carry the Classic? Cuz 180gr HSTs won't fit in the other one.