I would decide how many guns you want to put in it and then buy a bigger one.
I would also suggest getting a dial lock over a digital lock.
Then of course there is fire rating.
Is it made out of steel or thick sheet metal.
Personally I think any quality gun safe will keep the ordinary thief out.
if it is a true professional thief they will get into it , but more than likely won't be doing random home burglaries either.