The funnest supports in my opinion are:
Blitz,
Thresh,
and TAHM KENCH IS UNBENCHED(you gotta love eating people am i right?). They are all also pretty good.
The funnest top laners in my opinion are:
DARIUS,
Jax(at the moment anyway)
and Tahm(still gotta love eating people am i right?),
Another fun one is Riven but you gotta dedicate A LOT of time to learn and get good at her and then it gets fun.
Im just gonna list champs for the other roles also because why not.
Mid:
FIIIIIIZZZZZZZZ
Zed(takes time to learn)
Leblanc(takes a little time to learn)
and this one is kinda pretty bias but i believe Lulu mid is really fun
Jungle:
LEE SIN
Nidalee
Kindred
Quinn( at the moment anyway)
and this one is also pretty bias but Malphite jg is fun for me
Marksman:
Jinx(Slightly OP)
Twitch(OP)
And Lucian(OP)
Oh and all the champs that i put in all caps are my favorite from that lane.