Before I purchased my first safe I talked to a vendor at a gun show. He had retired from selling safes and strongrooms in Hollywood. His advice made sense. He claimed that all the brands of safes would be good enough, unless one had some really valuable stuff (like $1,000,000 in bearer bonds). If you had that and the right person found out, the best safe in the world would probably not be enough.
He did recommend that you secure the safe to the floor. Otherwise you may come home to find that after the local druggy smashed the handle and dial, he still couldn't get it open and ended up tipping it over in his rage, scratching your guns.
My only other advice is that the installation is a big thing. Gun safes are heavy!! My present man cave has a very small door. (The house dates to 1905) I couldn't get a standard safe in. I did some research and found Zanotti Armor on the web. They make safes that come apart into pieces. Not only did the pieces fit through the door, one or two men can easily handle them. I noticed last month that they now have competition.
I thought long and hard about electronic locks vs. mechanical. Yes, I know you can replace the batteries from the outside, but I decided that I didn't need another thing to go wrong when I really wanted to get into the safe. I went mechanical.