Gumal Ngurang is the best... it has the best location, it is the biggest, and it is the newest.
Bulga comes second.
I lived in a 4 bed apartment at Gumal and it was good, a lot of it rests on who you end up living with. If you want to make friends and want it to be social I would probably recommend living in the bigger (8 or 9 bed) apartments. You have extra bathrooms, much bigger kitchens and are probably less likely to tread on the toes of others than in the squishy 4 bed apartments. The social life at the residences isn't huge, it's what you make of it, but some of the res events like resball are excellent and the people are generally friendly. You sometimes get a freak flatmate or whatever, but that's life I'm afraid.
I'm moving back to Gumal when I come back from studying in London, and I'm probably moving in to an 8 bed apartment this time for something different.
It's a pretty good setup at Gumal, and an excellent excellent convenient location. Geegal is pretty far away from uni and it's hard to get home to Geegal at night safely. Apparently they are renovating Bulga at the moment, and it is just around the corner from Gumal, but it is a bit smaller and has less social life so I am told.
Any questions ask away, if I don't reply PM me cos I am starting my course in London on Monday so I probably won't be on here very much.