What Backwoods said.
However, I do make a couple of suggestions (imagine that):
Mechanical locking mechanisms are almost bulletproof. If it's a quality-manufactured mechanism, it'll last forever. Why mess with that? Convenience?
What happens the time you need your weapon(s) and the battery is dead? Most secure digital or biometric locking mechanisms DO NOT have a mechanical way around them. You'll either have to replace the battery or, well. . .die.
Electronic locks are great, for businesses or situations where the safe is frequently accessed (as in once or more a day). Other than that, it's just pure laziness to "need" an electronic lock because you want the "convenience."
A burglar doesn't care which lock you have, in all honesty. If he's good enough to get into the safe, the lock doesn't even matter. The mechanical lock only adds an advantage if the burglar is an experienced safecracker (i.e., he can open the lock by listening to the tumblers) and has a bit of time. Most will chose to learn what type of safe you have and "hard" crack it (drilling, cutting, etc.).
My other issue against electronic locks is that if you have a fire, you're screwed. You WILL have to call in a locksmith to open your safe if it survives. The electronics WILL NOT survive the same heat level as the rest of the safe, or it's contents.
In most cases, some penetrating oil and a bit of elbow grease will open a mechanical lock, if the heat didn't fuse the mechanism (but then. . .chances are you will only need to access the melted and charred remains of what's inside for proof to the insurance company, anyway).
So, my recommendation is that unless you constantly access the safe 3 or 4 times a day, go with a mechanical lock.