Well NiMH batteries for cars are all 7.2v and most that you will get online and hobby shops in aus will have the tamiya connector on them. The only real factor is the mAh rating. The bigger the number, the longer they will last for. So buy the biggest number you can afford.
The only thing to consider when buying them is if you do what i did and buy a good charger and a couple of batteries only to turn around a few months later and buy a whole different set up (ie LIPO) then you would have wasted a bit of money.
Brand wise, team orion and lrp a kinda brand names, but for the car your grabbing its not going to matter if all the cells are hand picked to work with each other and blah blah blah because your not yet running that in comps and stuff.