I really beg to differ on this one guys. The crosman .2gs are actually VERY good for the price. I've never had a single jam in my 50,000 rounds spent on those. Granted a high quality .25g will give you better accuracy, but where i live they are twice the price.
I would however stay away from .12g as they have low quality and could mess up your hop-up and barrel especially because G&G's come stock with a tightbore as i remember.
IMO the crosman .2gs are the best value to accuracy ratio out there, as you can get nicer bb's online for cheaper than locally but shipping just takes away any deal you might get.
As for higher quality bb's, i sometimes use TSD .25gs and they work nicely, just not worth the double price. IDK if you can get those in Canada though. As concerned with weight, .25g's are slower than .2gs, and .23gs are in the middle (the more weight though the more accurate). I would try all three and see which ones you like best.