The competition was actually for a different type of level (non-multiplayer) quite a while ago. I also came high in the co-op multiplayer competition, but I don't think they did badges for that!
I backed AGK, but I must admit I haven't really used it much. It really depends on the sort of thing you're after, AGK is much more done around code, whereas GG doesn't need any coding knowledge at all (unless you want to do lua scripting which is optional anyway). AGK isn't too hard to learn the basics, and there are plenty of examples included (of concepts and games).
AGK is good if you have an idea, and want to develop for a range of platforms, and GG is good if you want to quickly build something to play around with. I've not used AGK for 3D, though I believe it has some capabilities there - I'd think of AGK more focused on 2D apps.
Custom Mac Pro (2014): OSX 10.11 (El Capitan) and Windows 10 Pro:
Xeon E5 v2 @ 3.7Ghz ; Dual AMD FirePro D500 (6GB GDDR5) ; 12GB RAM ; 512GB SSD ;