And @Rolex's wax...
Seriously though, try and stick to name-brand batteries as has been mentioned. I've used Max Amps, Venom. Flight Power and Traxxas branded packs with no complaints.
I would get the LiPos, personally.
I'm not sure what a T-connector is, do you have a picture?
As far as power is concerned, are talking voltage? Depending on which rig that I'm running, I run either 2s (7.4v) or 3s (11.1v). I tend to run as high a capacity pack as will fit in the rig.