Top - Jarvan, a really good tanky dps and offers alot of utillity in teamfights. Can jump on carries and by the time they get out of all the CC and flash out, DEMACIAAAAA
Mid - Jarvan, especially when it is a weak AP carry, I mean you can just DEMACIAAAA and they can't escape
Jungle - Jarvan, he is such an allrounder and with DEMACIAAAA his ganks are deadly.
Support - This is a tough one...but I'll have to go with Jarvan, he suicide bombs onto the enemy and bursts them hard with DEMACIAAAAA only for your AD carry to finish them off and getting fed. Also with Philo stone, he has infinite harass.
AD Carry - I used to like Jarvan alot but recently I have been using J4 more, Infinity Edge and Bloodthirster and your whole combo does tons of damage, especially DEMACIAAAA