Eneloops, with a spare set of alkalines in the bag just in case.
Tip - the moment you detect the recyling getting a bit too long, raise the ISO and/or lower the f/number. One stop of either of those settings halves the flash output, dramatically cutting the recycle time and extending battery life.
+ 1 for Eneloops, but with a spare set of ... Eneloops in the bag (why a spare set of alkalines? To me the whole thing is not to buy expensive alkalines any more).
I have 7 eneloop packs, in sets of 4 to fallback on 




