All depends on what you're developing. I'd argue that engines like Unreal are deeply unsuited to quickfire events like jams. Maybe it'll improve in UE4, but the iteration time is just too slow as UE3 is geared towards large scale production, and flexibility comes first. Not sure if Unity is any better, not used it enough.…
If you plan on a 3D game I'd highly suggest Unity over all other engines. Due to it's component based nature it's a lot easier to prototype with. However I'd suggest staying away from 3D for game jams if you're on your own, make 2D games instead. For 2D engines Game Maker, Construct 2, Stencyl, and Game Salad are all worth…
Unity took home the super-happy-friendly piece of software for the last 2 years running, and it's probably the easiest, quickest piece of software to get into. Before you go to the game jam though, I'd heavily recommend grabbing and familiarizing yourself with the editor (should be fast) and grabbing and testing the…
We used Unity for the Global Game Jam this year and it got us over the line with pretty inexperienced coders. I'd probably go 2d for the next one given that its quicker and easier to hammer things out and that's pretty much your primary concern when you've got a mere 48 hours to play with.