Ok, a few thoughts .......some you can do dry firing ....
a. how they fit your hand
Can you reach all the controls comfortably ( thumb safety-if there is one, mag release, decocker if there is one )...and can you do it without moving your grip with the primary hand. Point is, if its too wide - or too long to reach ( of if you've had a broken thumb ) maybe you can't reach the mag release without moving your primary grip hand.....and if you have to move your grip to release a mag...the gun does not fit your hands. Try it in the shop...dry firing....
b. grip angle ...
Grip the gun "high and tight" ....does it come up level / where the sights are level - or do you have to roll your wrist to get the gun level. Some guns will come up naturally - some won't . Eliminate the ones that will not come up right - grip angle is wrong. Again do it dry firing..
Now some guns - have back straps that you can change....
c. Sights....
Some are big and easy to see ...some not so much / night sights are a good thing in my view...but there are a lot of different styles.....some you'll hate, some you'll love....fibre optic, front gold bead, what dots, whatever....
d. weight and length ...overall and of grip area....
generally poly frame guns are light / short barrel guns are short...but depending on the size of your hands...some may fit you, some may not. Some guns have a bumper on the base of the mag - that give you a little more room to grip the gun with the small finger on your primary hand...if you need it ( like a Sig 239 model ) ...which makes a small gun shootable for some of us with bigger hands....
The lighter the gun --- the more recoil you'll get ....
The shorter the gun ...the shorter the sight plane you get...
Example...a Sig 239(single stack and shorter) vs a Sig 226 ( their full size gun double stack) ...weight, width, length of sight plane are both really differnet....and so is the Sig 229, etc.....
e. shooting them....
does the gun recoil in a predictable pattern so it returns back to your initial position for a follow up shot. Some shorter guns for me, in heavier calibers ..seem to me, to recoil almost in a figure 8 and are really hard to shoot.
f. Triggers.....
width, length or reach for you, how much slack, how much creep, how do they break ( 3.5 lbs, 4 lbs, 6 lbs, 10 lbs....) ....and even more important how far do you have to release them to reset trigger for 2nd shot. A 1911 has a very precise trigger - it moves straight back and forth in the frame ( no slack, no creep, breaks very crisply ...usually 3.5 - 4 lbs ...) if its well made...../ many guns, like Sigs, have a trigger that is suspended from a pin ...so as you move it back and forth ..it moves thru an arc.../ some triggers almost wobble left and right as they move ( those really aggravate me) ...but it depends on what you like....width of trigger shoe / how it fits your fingers...all a big deal...
again some of this you can do at the counter - dry firing ...some you need to go to the range.
As I see it ....find a gun you really like / then compare each to that one...grip angle, how trigger feels, sight plane, sights....
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rent some guns ...( 1911's come in 9mm too ) so rent some, if you can ....and stay in the 9mm before you wander off into other calibers. Ideally you're looking for that one gun that just feels right.
note....a friend lusted after a full sized Sig 226...but when he finally shot it, it was just too big for his hands ...not his gun. Some of us are devoted 1911 guys ...and no matter what is new or different...1911's are where we stay ...but there is a huge range of 1911's from RIA, Colt, S&W, Springfield, Sig - to upper end guns like Les Baer, Ed Brown, Nighthawk and Wilson Combat.
Mix in some revolvers...guns like a S&W K frame ( model 66 ) in a 4" in .357 mag or .38 spl...and see how it feels. Maybe you eliminate the revolvers right away ...maybe not....
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last but not least.....make sure you have fun with the process.
If you have a buddy with a big collection....ask if you can spend some time with him or her....and go thru their collection...see how it feels, etc....it may help a lot...