I main top lane, playing Vi and Fiora. But I want a secondary role in case I lose top in the queue. All in all, my playstyle is to kill things, generally by diving in. I like to be mobile and tough, but value damage above all things. I want to play mid for it's massive damage and team carrying ability, but I'm worried about mid laners with no mobility . Would the damage offset the mobility in mid? My problem with jungle is that I want to be getting kills, not just supporting my team. Please, help me decide with a description of why. Thanks.
I'd say just try out both roles with a variety of champs and see which one you prefer. No one can tell you what you like to play and that's the biggest thing because if you don't like playing it you won't succeed. Not all mid laners are immobile damage machines, not all junglers just support their teams without carrying potential, just try them all out.