I have a G38 and have about 800 rounds down the pipe. I also looked at the 30, the 36 and others, but I found I did not like the short grip on the 30. When I dropped a mag and inserted a fresh one, my hand got pinched.
So far I like my 38 (as much as one can actually like a Glock) and it has been 100% reliable and very accurate. I put a Ghost rocket trigger connector in it, changed the sights, and will be doing some work to the grip and trigger guard with my drumel tool here very shortly. I took it to a class last weekend and it put a nice blister on the knuckle of my social finger, so some re-shaping is in order. The Rocket trigger is the best I have ever felt in a Glock, I hear other after market connectors are good as well. As for the ammo, I paid a bit over $12.00 a box for Lawman on line. It is more than ACP ammo, but so are a lot of things, $4.00 per box more seems like a lot, but for someone with a $1,000 1911 to bitch to you about the cost of your ammo in your $450.00 gun seems a bit short sighted.
The GAP is a good round, and had it come out before the .40 things would be drastically different, but it did not. Long term success of the round is in the hands of Law Enforcement, if they adopt it, the round will do well, if they don't, it may be a might have been, but since the bullets needed to hand load it are the same as ACP you should be able to shoot a GAP for a long time.
Good luck on your hunt.