As a part time lock smith I can assure you no safe is 100% thief-proof. A determined thief with the proper tools WILL get into any home safe, given enough time. IMHO the purpose of a home gun safe (and mine looks a lot like the one in the picture
) is to keep unauthorized people and the run of the mill burglar out and to provide some level of fire protection. If a professional wants my stuff there is very little I can do to prevent it. That's why I have all my firearms specify listed on my home owners insurance.
By placing my safe in the basement, bolting it to the wall and floor, placing it to make an attack like the one in the picture difficult, and adding bags of lead shot to add weight (the safe is now too heavy for the steps out of the basement to support) I have done all I reasonably can to protect my stuff. I'm at the point of diminishing returns. A more expensive safe won't add enough protection to justify the costs.