2xAA, almost certainly; being on the road, having access to the ubiquitous AA cell for refills is paramount IMO.
My emergency car light kit utilizes 2xAA LSD NiMH (i.e. Eneloops), with lithium primaries for backup.
That way, it's 'guilt-free lumens' & free recharges after use, but always having lithium cells available in case things get rough.