Most of it doesn't matter much. I look for ambi safeties, because I'm left-handed. They don't have to be huge safeties, just your standard ambi safety that's on about every gun that has them.
Front strap checkering, while nice, is not a big deal because I can toss a little grip tape around the front strap and it's good to go.
Forward serrations are helpful sometimes, but generally, especially in minor guns, the gun is sprung so soft that racking from the front is not an issue even with a slick-sided gun
The only thing I even look at anymore is the safeties and budget. The safety's obviously can be changed if they need to be.
If you look at a gun like a Springfield loaded model, it will have basically everything you need. If that was too expensive you can buy a Rock Island that has the same features. If neither of those are "good enough" you can buy Dan Wesson or Wilson or full custom. Throw a trigger job on any of those guns and you'll be pretty happy
Edited to add: I don't worry with rails because it makes holsters harder to find. I can't remember what they bumped the weight up to for single stack, but that might be an issue with a rail, but it completely may not as well. But if it wasn't an issue, and you can find a holster easy, I do kind of like the way they look