needle bearings look like little needles that roll on their sides

roller bearings are ball bearings

cartrige bearings are in cartriges that justdrop in (not loose balls, etc)

Sealed bearings are sealed cartriges that just drop in

For less maintenence, go with sealed cartrige bearings. You don't have to re-lube all the time like non-sealed. And when they wear out, you can just drop new ones in.