What champions are enjoyable differs greatly from person to person.
As an example, I tend to enjoy:
- Siege casters (i.e. Varus, Corki, Ziggs, Jayce, Morgana)
- CC Tanks (i.e. Gragas, Sejuani, Zac, Nautilus, Maokai)
- Fighters (i.e. Irelia, Renekton, Nasus, Trundle, Udyr, Volibear, Shyvana )
However, if you asked somebody else, then they may say that my picks are boring and that ADC, supports, or assassins were the most enjoyable.
Also, I would highly recommend shrinking your focus. Try to focus on ~3 champions in two roles. You will better learn how various match-ups play out, what weaknesses/power-spikes you can exploit, what role you are supposed to fulfill at various points of the game, etc.
Learning how every role plays and knowing how certain match-ups should progress is very helpful even when you are playing other roles, but work your way up to it.
What champions (specific champions or general archetypes) do you enjoy playing? What are your preferred roles?