I think they all have pretty good communities. I only have experience with Unity, but I would say it's more or less all right, depending on how you feel about real time shadows, which only comes in the pro version. The main advantages are that they get it running pretty well on phones and tablets, although ports are expensive. I think the android port is still free right now. I'm really only using it because I can put the game on Kongregate when I'm finished. The best thing to do is actually join the community and ask a few questions, see how you do for responses. Unity is pretty excellent that way, plus there are a huge number of free tutorials around. I don't know what the editors are like on the others, but Unity's are excellent. Importing from most major modelers is also very easy, including Blender, which is a good free option.