1) 1 had a bunch of eps I think were great. stuff like School Spirit, Monster Arm, and Diaz Family Vacation are super fun even if to some extent they have more generic characters/settings and are more standard cartoon plots. Quest Buy, Freeze Day, and Storm the Castle are similarly good but for worldbuilding/LORE.
not gonna touch 2 for this comparison since you just mentioned 1 and 3 (2 is my favorite season and I think it has a comparable number of great eps if not more), but I don't think 3 has done as many eps that stand out to me as much. Toffee and Sophomore Slump are great, some BfM eps and the sleep-portalling stuff come pretty close too, but mostly this season ranges from average to mediocre to just bad for me. for 1 the only episode I think is really bad is Banagic (maybe Pixtopia too on a bad day), while I can aname off a bunch of S3 eps that to me totally failed at what they tried to do
because S1 had simpler goals, it had less to try to accomplish within a single episode and thus tended to fail less.
2) this is pretty subjective but I think 1 might have been the funniest season. 2 was better as a whole taking into account characters/plot/emotion/etc., but 1 is still the most memorable/quotable for me
3)Toffee is used best as a threat in 1 and is still maybe the best villain (not character). Ludo was great too, the better character and part of the reason 2 is as good as it is, but is mostly absent from 3 and is a less of a villain in BfM since Toffee is the focus; Eclipsa is ambiguous; Heinous could be good too but it's too early to say.
the show can never again recapture that sense of characters in an episodic comedy realizing they're facing a dead serious villain who totally outmatches them and doesn't play by the rules they've followed up to now. the season as a whole has a great twist of getting more real by the end that later seasons can't recapture, as now everyone expects drama and serious moments and twists
4) less ship bullshit