Trying to find a main....

Hey there , after playing league for a long time I finally thought about maining a champion at first I chose Talon, then Anivia, and now Kassadin so  after a while people told me why not just play all of those champions and I guess they are right because I do enjoy them all but I just cant manage to fit them all into a single game and I don't know who to choose . Right now i'm even messed up top lane I don't have a real main champion there , right now i'm torn between Nasus, Garen, and sometimes Vladimir but I kinda gave up on him because I am horrid at him and always feed. So basically in conclusion I need some help on what champion i should be maining right now , i'm leaning on Kassadin because i love him mobility late game power and stupidly over powered burst damage.