I played through all of them in order just last week. (None of this start with 3 weakling nonsense).
My favourite is definitely 3. Crash 1 is hard in a Mega Man 1 kinda a way where deaths are cheap and plentiful. It is bottomless pits galore. Crash 2 is better but is still cheap in a few places but the level design is better. Crash 3 has some really great levels and I like all the vehicle levels except for the motorcycle ones. (It plays much worse than Mario Kart). Also, Crash 3 has no cheap deaths so the experience never feels frustrating.
Also no I do not like Crash 3 the most because it was easy. The original creators of Crash had no clue how to make a hard platformer without being cheap. If you want to play a hard platformer that is not cheap. Get the Donkey Kong Country games or get play Super Mario Bros: The Lost Levels. Those game are proper ways on how to make a hard platformer.