To echo what everyone else has said, LiPo is worth the cash and the hype.

I tried running Maha brand (one of the best) 2700mah Nimh AA cells in my brushless mini inferno (even after upgrading the wires on the stock AA harness) with abysmal results. It had very little pick-up and a pretty low top end. The discharge capacity just wasn't there.

Now I run twin Apogee 3s 1000mah 20C packs in parallel - max continuous discharge of up to 40A. The batteries and motor (wraith 7k), unfortunately, overpower my ESC (thermal shutoff). The top end is crazy fast and the pickup is incredible.