A good rule of thumb is the safe will only hold half of the guns advertised. As far as what is best is just a rabbit hole that you don't want to go down. Firstly, there isn't really a set standard for gun safes. So what that means is that manufacturers are free to test their product however they see fit and label it as such. Fire ratings are a big one here, you'll notice that safes have different tested temperatures and methods. If it has a UL rating, which is an independent tester, then it's usually pretty good. I spent two weeks in a course for SSE where we learned how to open safes, obtain hard drives, files, etc, etc. What I learned is that most gun safes are extremely easy to get into. Most gun safes can be opened in just a couple of minutes unless it has a a higher UL rating. So unless you got real deep pockets, you can't get a safe that will prevent burglaries. With that in mind, I would mainly look for fire rating and size. Those are the two biggest things to me. Whatever you end up with please do yourself a favor and bolt the safe to the floor.
