It’s not the size it’s how you use it.
The best sets have a strong, cohesive theme that brings all the cards in the set together.
Team Rocket, Neo Destiny, basically all eseries, Sandstorm, Delta species, pokekyun, even Evolutions and Hidden fates to some degree. They all have the same thing in common.
I think the Japanese Vending Series + Masaki promos is the perfect set size
So, the answer to this question is: it depends. Most people here seem to be favoring smaller-medium set sizes. However, I think it depends on the art. Skyridge, aquapolis, expedition had amazing art consistently and are highly sought after, yet they’re also the largest sets. With more recent sets (which tend to be large), many people think they have bad/mediocre artwork - so they don’t like those sets - not because they’re large, but because the art is meh, and the rares are overprinted/have too many variants, or have a bad pull rate.
Small (around 120 cards and under is perfect) with a few sprinklings of secret rares, not the 30+ we’re getting in every set.
the three eseries sets are perhaps the best themed sets in all of the tcg. They look like a route in one of the games with all the pokemon you’d find there. No other sets come close
amen
I think smpratte better encapsulated this issue in his recent video. I’m not sure it’s inherently small sets that I prefer but it is clear that many recent modern English sets are poorly constructed. I think the fact they are also large goes hand-in-hand with that though.
Think it should be as large as possible without compromising quality and identity
Very good for home deco if you need a centerpiece
Imagine having a complete alpha set framed on the wall
I thought long and hard about this since the topic went up because I actually was not sure what I thought.
After a lot of reflection, I think my ideal set would be:
-Around 75 unique cards
-No duplicate art
-Limited duplicate Pokémon
-A cohesive theme
-Vintage set numeration
Unfortunately for me, there are no sets in the WotC era that meet this criteria. Some are close. Rocket has 84 cards and one of the strongest themes of the era, but is full of non-holo duplicates that offer nothing to the set. Neo Revelation has 66 cards and all of its non-holo rares have unique art. The theming is pretty good in being centered around legendary Pokémon, although it’s not my favorite theme.
But I like these two sets a lot because they are closest to my ideal sets.
I think the non-holo artwork for Team Rocket (not counting the holo duplicates) is stronger than Neo Revelation but I think Neo Revelation has arguably the best holos of any WotC set. The 3 Dogs, Ampharos, Houndoom and Shining Gyarados are all top tier.
Small for sure. I love being able to actually compete sets. Smaller fits better in binders and easy to just crack packs and complete. A lot of sets now a days make it hard to complete which I think makes me want to turn away from. Japanese sets are normally small and easy to collect and if you wanna grade, they grade better than english. Same art work for fraction of the price as well. Though I do love the alt arts but just planning on buying the ones I dont pull from a few boxes.
Anything bigger than a handful is a waste, personally.
Smaller for set collecting for sure.
Battle Styles was the first English set I’ve opened up a good amount of product for in a long time. And I did make a binder for it, but decided to just skip the alt arts and secret rares for the set since that makes it so massive and pricey and I can focus more on completing the old sets I like better. That way I can just get the few secret rare and alts I want without feeling the need to get 20 rainbow nonsense cards I don’t. I’m gonna do the same for chilling reign.
That way I can also fit more than one modern set in one binder.
Small. The crazy size of some of the recent sets has had me like what the heck. 
I think it makes it to overwhelming. I want to be done by the time the next set comes out. 