I mostly use Samsung 30Q’s, because they’re a good general purpose cell for just about everything.
I use Sanyo GA’s in lights that I want a bit longer run-time, and are single-emitter lights (so less than 10A drain).
I use Sony VTC6 in high-drain lights. They’re slightly better than 30Q’s, though in practice I doubt it matters.
I still use some old laptop cells in some lights that I don’t run at max output. Though, this is really just “because I can”. I should probably just use 30Q’s in these.