NiCd's is easier to maintain, takes more abuse and seems to last longer. However, NiMh is avaible in larger capasity.
Some people claim that NiCd's got more punch, however, I prefer the performance from NiMh. I find they have plenty of punch for stock class, which I'm driving exclusively.
Schumacher Mi5 - Sanwa MT-4 / RX-462 / KO Propo PDS-2123 - Nosram 5600 X-treme Saddle Pack - LRP SPX Zero/X12 17,5 - Nosram Stealth Touch Evolution - MAAS SPS 9250