Between those two, NiCd all the way. They are a little bit heavier, but more durable. Buy welded packs with Sanyo cells.
Hangtimes Hobbies is a great vendor.
That said, all my flight packs are now LiFe. I buy the soft type LiFe 1400 mah packs for everything but my 50cc Sukhoi 26. LiFe packs are lighter, about 1/2 the price, don't self-discharge, and can handle more current draw. they don't hold up like NiCd's, but I do a 2 year replacement cycle which puts my actual cost about the same as the 3-4 year cycle I used to run with NiCds. I paid $13 at Hobbyking for the charger I use for them.