Who is most fun to play and who is most viable?

hm good question, both are fun and viable. I myself prefer nocturne as he is more fun to me. So i voted for noc.

I have both of them, but I enjoy more Jarvan IV. The tanky DPS against squishy assassin. I like them both, but i feel like jarvan and I are on the same wave.

I dont have jarvan but i seen some people that mastered him kicking the ass of nocturnes and jarvan is more viable and is really fun

Jarvan, by far. Just the fact that he can yell "Demacia!" proves this.

it depends ... jarvan is typical tanky dps able to deal decent damag without sacrificeing survability representing current metagame to the core with hard to use properly ulti ... (most epic ulti: we wanted to ambush the enemy so we waited for them to come, after a while rammus and nunu entered our bush, jarvan ultied us all and nunu/ rammus started their ulti, 2 sec later fiddle joined in ... gg)

On the other hand nocturn is champion very symilar to jungle yi, annoying ganker with stronger dmg at the cost of lower survabiity which shines brightly in the early/ midgame. suit yourself ...