What's the best position to play to climb elo? (Jungle, Solo-top, AP Mid, Support, Ranged AD) Been losing quite a few games lately, and I mostly play support in Ranked but is there any one position that has a better chance at carrying a team to victory?

AP mid or jungler.

In my experience, at low to mid elo, the jungler.

That way you can babysit all lanes and generally is your duty to do so.

What would you say is the best jungler for low elo? I've been practicing some junglers lately, with some decent success on Amumu (in normals anyway)

Jungler or Solo top I'd say personally. Jungler makes a huge impact on how the game goes. No matter how much your team suck, if you have enough successful ganks, they'll probably be fed enough to at least do something. As for solo top, you are just alone and usually tanky so you aren't worried too much about anyone else taking your farm etc. Farm up and carry your team. The only thing I find about AP mids is that you are usually too squishy and gets killed too fast to carry.