Which lipos for 9xl & 9920? Please help. 10c?15c?20c?

I have a Gmaxx I've been building and I'm in need of some advice. I have a 9920 esc with a 9xl motor. I have the single speed conversion on my maxx. My question is what can I run for Lipos? There are so many options. My biggest question is can I run 10c or 15c or do I need 20c batteries. I know I want to use 11.1v 3s 4000 mah packs but I don't know what the difference is between the 10c,15c or 20c versions of them. I know price is a big difference. Could someone please help. Thanks Guys.