I'll probably use GameMaker: Studio, as that's what I'm most familiar with. I'm trying to learn Unity at the moment though, so if I'm feeling comfortable enough with it by the time the jam happens I guess I could try that!
Learning Unity is on my list of things to do, too. I feel like 75% of it is just... figuring out the right menu configuration/best workflow haha. Can't wait to see your game!