[Chojin]

pyro, soldier, and demo are easiest imo, sniper is also easy to pick up if you've played a lot of FPS games

heavy and engineer are also easy but require a bit of learning (teamwork & ubers VS how to build shit and where to build it)

medic is easy if you're just pocket medic to one guy, but being a good medic can be pretty challenging.

scout and spy are the hardest, but scout is about reflexes and spy is about outsmarting people. both classes also require knowledge of the map and some planning skills.