Well, I guess I'll be the bad guy on this one. I carry a Para P-12 most of the time, and am thankful for it saving my life, so I'm prejudiced. I've also got Rock Islands, Springfields, and a Witness from Tanfoglio that's "adaptable" to both .45's or 10MM.
Workiing in a gun store, I've learned a lot about the different guns on the market, and found out an interesting fact some time back. It seems that the Phillipines is the 2nd largest gun market in the world, and there are scads of 1911's that either are built in the Phillipines, or were being manufactured there and moved to the U.S. One of the best concealed carry 1911's I've run across was a "Citadel", manufactured in the Phillipines. It was compact, carried a full load of ammo, and seemed to function every time the trigger was pulled.
I've owned S&W's 4566, and loved it. The mags were being recalled when I had mine, so I traded it until all that blew over, and just never got another one... but I loved that gun as well.
I've got an XDM (but not in .45), and they're as reliable as any gun I've owned... so the answer to your question is "go buy one and try it"... there are a lot of good .45 pistols on the market, and there's no "one answer" for your question... it's the gun that feels best to you, and functions when you pull the trigger. Right now, I own 5 different .45's of varying manufactures, and they all function fine. I'm not afraid to carry any one of them at any time.
I'm impressed by Para's G.I. Expert, but don't own one... but for the money, it seems to be the best "new" gun under your $500 budget. Stoeger's "Cougar" is another one that I've owned and find to be an awesome gun to shoot. It appears to me that the Cougar has a perfect grip angle, and the gun comes up perfectly in the sight plane for your target. It's bulky as a concealed carry piece, but it's a hell of a shooter.
I'd like to recommend a Kimber to you, but my experience with them was negative. "New" Kimbers seem to have the kind of problems other guns develop as they're shot... i.e. FTF's and stovepipes... now maybe they cure themselves as they're used, but (as I said) my experience has been negative with them, and I think they are more "cult" guns than actually "excellent" guns... When I ask customers why they want a Kimber, they always give me the answer... "because it's a Kimber". When I ask them what makes it better than any of the other guns... they keep to the mantra, but can never point to anything about Kimbers that isn't found in the other guns... so I think they're way over-rated.
I don't recommend Glocks because I've never found one that fit my hand. I know they're reliable, and have a cult following also, but I'm just not in the club.
WT