I bought the first seven volumes in a bundle (I didn't get hip to these sets until the first six had already been released), and worked through them at a steady rate over the course of a few months. Watching them that way, you can easily plot the boys' quality curve over time, especially if (like me) you hadn't seen these shorts for years and don't carry any particular biases. Here's how they played out for me:
Volume 3: Really a toss-up between this and the previous set. These sets reaffirm the conventional wisdom that 1937-1942 saw the Stooges operating at full power. Every aspect - writing, performance, production values, rhythm - is top tier stuff. V3 barely edges out V2 on grounds of personal preference, for inclusion of shorts like Plumbing, How High is Up, and Ache in Every Stake, and also for the complete absence of Charley Chase in the director's chair (sorry Chase fans).
Volume 2: See the above comments for V3. The inclusion of all the Chase-directed shorts (which I found a bit too mawkish and gentle-handed, like he really wanted to present the boys as adorable little clowns) dilutes this one a bit, but this set still has one of the highest concentrations of prime shorts. After three years on the job the boys are in the groove, rocking like daddies, and at this early stage the gags haven't started repeating themselves too egregiously yet.
Volume 1: One of the most surprising revelations while watching these shorts was seeing how good Larry was in the first three years. By the next volume of shorts Curly would go nova and Larry would be relegated to the background to make room for the Jerome explosion, but on Volume 1 he's given equal footing with the other two, and the grace and precision of his performance was an unexpected delight. I'd argue that 1934-1936 may be the only years Larry could be said to have actually been performing, rather than just reacting instinctively to the mayhem going on around him. As for the shorts themselves, although you can see the boys (and the production team) trying to find their rhythm in these earliest shorts, they settle in pretty quickly, and it's fun watching Curly's confidence grow as you work through the shorts on this volume.
Volume 6: Shemp Howard inna house! This volume was like someone opening a window and letting in a cool breeze after the dreary Volume 5, and the aqua blue color was a soothing balm for my post-Volume 5 anxiety. Shemp has settled into his Stooge persona nicely by now, and gives what may be his best performance with the Stooges in Who Done It? The many Shemp shorts on this set that were new to me made this one a special treat. The inclusion of a few (non-stock footage) remakes hints at the creative well starting to run dry, but even these don't detract much since Shemp manages to give these old scripts a fresh spin. And as Metal mentioned, it's fun watching Burns run rings around White with his more thoughtful handling of the material.
Volume 4: Still a great set of shorts overall, you can see the boys starting to come down from their Volume 2-3 peak just a bit, particularly starting around the halfway point. And of course you can sense the ill-winds coming with the last few shorts...
Volume 7: A few scattered standout shorts and some 3D novelty, but it's all going stale at this point. Cheap sets, gags we've all seen a dozen times before, recycled footage galore, and Moe's eye-bags are bigger than ever. I admit it, I enjoyed Choo Choo. Crazy-ass short, but the experimental direction felt so much fresher than most of the other shorts on this set. The fact that I watched this set at the tail end of a chronological multi-month Stooge marathon probably doesn't do it any favors. The repeat gags are more evident, and I was probably suffering from Stooge exhaustion by that point. But there's no denying that the Stooges were pretty much out of gas and coasting to the end by this point. Can't help but wonder, though, how this set of shorts would rate with someone who wasn't familiar with the Stooges and didn't know they were looking at 45% reused footage.
Volume 5: Pretty unpleasant viewing. I rate Three Little Pirates higher than it probably deserves, only because Curly was mostly conscious and almost competent throughout the whole thing, which can't be said for the rest of his shorts on this set. Watching Curly on this volume is like watching your kid act in a school play...you're on the edge of your seat, rooting for him and wanting so much for him to get it right and not embarrass himself, yet there he is missing his mark, delivering his lines uncomfortably, and needing a prod from his fellow actors now and then. And all you can do is squirm. Matters are made worse by the some of the worst material the Stooges have ever had to work with. Shorts like Beer Barrel Polecats, Three Loan Wolves, and (dear god) Rhythm and Weep make the first half of this set the Stooges' absolute nadir. The arrival of Shemp half way through this volume at least gives you a sense of relief after watching a barely animate Curly struggle through the first half of the set, but as great as Shemp is, it takes him a few shorts to get revved up. At least you get the superb Brideless Groom on this Volume, which is probably the highlight of this otherwise depressing set.
Volume 8: Not sure I'm going to pick this up, to be honest. The writing was on the wall with Volume 7, and I'm not sure I need a set comprising mostly recycled Shemp footage and and a few contractually obligated shorts where everyone is pretending Joe Besser is an adequate substitute for a Howard brother.