Well, as Dan said, it all matters if the GM is active or not. If he isn't, well, you've pretty much got yourself an inactive guild there, with pretty much no hope. Also, like Dan said, why not post on that nifty forum for your guild, and see whats going on, and if there are any plans to get the guild active again.
If you decide to leave, at least take the oppurtunity to friend the guild mates you like the most, so you can stay in touch in-game.
And lastly, finding a new guild. I'm not gonna sit here and tell you how great my guild is, our how this guild is good, or that guild isn't. How guild a good is depends on YOUR opinion. Don't let others tell you what guild is the best, based on members, the leaderboards, etc. Take a look around the forums, and see which one best suits you. I'm sure you'll be able to fid one
Good luck matey!