Normal playthrough:
Easiest: 3, assuming you don't mind the vehicle stages, the fact that crsh gets powerups makes pacing fairer, heck, you get a BAZOOKA as your last powerup and the final fight is so easy i could win with a Hasbro joystick
Hardest: 1, i would write a entire Retorspective Article about the game's poor aging, but if you hate a mechanic of that one, then that's an argument
100%:
Easiest: 2, the hidden gems can be picked from the get go instead of being made to get Time Trials (AKA play the same stage twice) and the hardest skull route is still mild compared to the easiest ones from Warped (Or even some regular ones from Crash 1)
Hardest: Once again, 1, not even N.Sane Trilogy makes it easier, true, boxes works like in 2 Onwards, but the Color Gems (AKA THE ONES YOU TRULY DON'T WANT TO MISS MERELY BECAUSE YOU DIED) they brought it back, even giving a special message if you get all boxes but died as a last fuck you