My question is which do you think is easier?
I get this question a LOT and this is the best way I've come up with to answer it: The backroll is easier to learn, BUT once you've learned the tantrum and backroll, the tantrum is easier to do. There a couple good reasons for this. The backroll uses an edge through the top of the wake, like a w2w jump, which you already know, unlike the tantrum, which is a 'trip-flip'. But once you've learned them both, on the tantrum you can spot your landing super early, so IMO they're easier to do. Good luck!