I have a Glock 23 right now, along with a Kimber .45.  I would like to get a Glock in .45, but nothing looked good to me until the .45 GAP.  Does anyone have any suggestions on this caliber?

we don't know if this is his first handgun.

What i posted in another thread:

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Here's my opinion on .45 GAP. It allows you to fit 45 caliber rounds into a 9mm sized pistol. This comes with a sacrafice of capacity. Guns in .45 gap often have nearly half the capacity of their 9mm cousins. Some people will claim that because your shooting a 45 you need less rounds to get the job done.

This is bullshit.

The truth is that all common service calibers using quality hollow points perform essentially the same. A tenth of an inch of expansion and an inch or two of penetration. The difference between the terminal ballistics of a 9mm and 45 using quality loadings is not enough to make a poorly placed shot good or a well placed shot bad. A hit is a hit and a miss is a miss. The 9mm gives you twice as many chances score that critical hit while your adrenaline is pumping and your running and weaving and shooting in less than optimal conditions that are common in real life.

The other less noteworthy advantages that may or may not be a factor for you is lighter recoil, more common caliber, cheaper practice ammo, etc.

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So, do i think that there is an advantage over your current G23?  No.  Not unless you would rather carry 9 rounds instead of 14 in a similar size package (note that while the frame dimensions are the same as the 9/40, the slide thickness on the 45 gap is the same as the 45acp glocks, not the 9/40, so you'd have to get all new holsters too.)

I have a G23 & G38 -  I like the G38 much better, and use it for a "beater" CCW (car, backpacking etc.).  I save my kimber for the range, house & sometimes CCW...  If you want a G19 sized 45, I would recommend it.  

I own ten Glocks, nine of which I shoot fairly regularly.  The other one is still sealed in the box.  Well, I guess I should say, I used to shoot them all regularly.  I have pretty stuck with shooting my G38 lately.  I have practiced with the 9mm a bit also, but it doesn't get the blood flowing like 45 does.

As of right now.  The only draw back to the 45GAP no matter the make or model, is the availability and price of factory ammunition.  You can still find some deals and that is what I did.  I have been shopping around on-line and stocked up on some cases.  I have paid anywhere from $11 a box to $14 a box after shipping.  My plan is to stock up on the brass from this ammo and start reloading my own.  The way I see it, ammo prices are only going to keep going up with gas prices being what they are.

Other than that, all my guns in 45GAP(G37, G38, XD-45LE) have been perfect.  Manageable recoil, accurate and fun.

I went the way of the G21 and never looked back. Personally, I want to throw the largest bullet I can down range - the G21 give me that plus a 13 round magazine capacity along with mild recoil.

That being said, you can't go wrong with a G17 or G19 - don't ever underestimate the 9mm.

I'm a big fan of the 45 GAP in the Glock pistols. I own all three, the G37, G38 & G39.  The G38 is my favorite Glock by far. It is very accurate, controlable, and fun to shoot.   I have been paying a little over $11 a box for speer lawman 200g FMJ at a local dealer which I consider to be a good price. I think certain dealers just need to stop gouging on the price which would help promote the cartridge as well.

Here is an interesting thread on the GAP round.
www.ar15.com/forums/topic.html?b=5&f=20&t=17790