Nickle Metal Hydride packs generally have better runtime than Nicads, and they also get better on the 2nd and 3rd charge in a day. NiCads are much more finicky, you should really only run them once a week for max performance, and have less runtime generally as well. If you can afford the extra couple bucks, go with NiMH packs. The E-Maxx packs just come as a pair of packs for a little less money.