Silver plated copper is the way to go. And don't be using cheap house wire or the stuff you get at princess auto. Check out hobbyshops and see if they have really good stuff. Speaker wire won't cut it lol
If your redoing your wiring, you might as well buy a MOSFET. There's really no point to upgrading your wiring if your going to run it through your trigger, the difference in ROF won't be noticeable at all. And since your trigger is the highest point of resistance in your electrical system, it should be the first thing to get rid of.
The idea is to replace your wiring when you decide to go with a MOSFET, since you have to rewire your AEG anyway, you might as well do it properly. That's when having good wire can give you an extra 20rpm, but most importantly, more battery life. Oh, and use deans connectors lol
Even if you can't find a hobbyshop, just google for wire manufacturers. Lots of companies sell wire. And any high quality wire you have left after rewiring your AEG can be used as REALLY high quality speaker wire, and for a WAY cheaper price than what you'd find at retailers!