Similar to many others who have responded here...I've handled, owned, used several different GBB models from a variety of manufacturers.
Without a doubt, the TM HiCapa (either 4.3 or 5.1) works best for me. Accuracy, gas capacity, upgrades, etc...all those good reasons.
But instead of a specific recommendation...I'd recommend that you get your hands on as many different models as you can. It's a bit hard to tell the subtle differences between the same model from different manufacturers...but it's easy to tell which model feels best in your hands.
Some guys are most comfortable with Glocks, others with Sig 226, etc... Some just need to compensate for other shortcomings by going with a Desert Eagle (just kidding around...but you've got to wonder...
). And there are "compact" varieties for each model. The SIG 226 has a "little" brother with the 229...I can't keep track of the variations of a Glock with out a spreadsheet...etc...
For example the USP Compact fits my hands quite well...but the USP doesn't. There isn't a single variation of the M9/92F that I feel comfortable with. I've owned a SIG226 on at least 3 separate occasions...but just don't seem to reach for it when it's game time.
Once you get narrowed down on a model...then research reviews on each manufacturers make of that particular one. Some are fantastic...others are not.
The best bang for your buck with regards to a GBB is one that doesn't break.
They're overly complicated...there's lots of parts...the parts are not always easy to come by....
But man, oh man...are they ever fun!
Best of luck,