The first nimhs I had were 3000mah - unbranded that came with car.
I actually found these to be on the whole quite good. For a 2nd battery went for a core 5000mah, performance just as good, however runtime was vastly improved (at this point in time was only bashing in field and alley) in fact run time was so good - managed to melt the tamiya connectors.
Thats about the only exp I have on nimhs, unbranded performing just as well as branded, the only diff being the higher the mah, the longer the playtime
(not too important if you racing and have a charger with you tho).
I've actually taken a step even further back than nimhs and running nicads in one of my mini's