Personally, I’d say haste is better since you need it to mine while flying. High levels of efficiency don’t make a huge difference unless you spend a lot of mana, and trench needs little to no levels of efficiency to work effectively.
Personally, I’d say haste is better since you need it to mine while flying. High levels of efficiency don’t make a huge difference unless you spend a lot of mana, and trench needs little to no levels of efficiency to work effectively.
I don't fly and mine, but I've tried both (I'm starting out on Aether presently), and haste definitely seems more helpful; it's cheaper and seems about 2x as effective.
If you want to use your pickaxe for things other than mining, additional haste levels will let you break non-primarily-pick-minable blocks (e.g. wood, sand, cactus, glass), faster. Additional levels of efficiency do not help you break blocks that the tool is not designed to break. So if you need to clear a bunch of poorly placed glass, your best bet is doing so with a haste 20 pick.