I have used a couple different ones over the years. The place I have now had them installed on the shop and house, these were the mechanical ones. They seemed to be pretty durable, but a few years ago I put the new equivalents on at my parents' place and I had to replace them after about a year as they got too stiff for them to unlock. Still don't know what the issue is/was with them, they were the KABA brand.
I had to replace one of the mechanicals at my house and both of the ones I put in at my parents' place and I went with the electric (internal 9V battery) version. Did that in 2012 and had mine fail on me just a few months ago, I replaced it with another electric one. The Schlage version costs about $120 from Menards.
Personally, I love the things for their convenience. The down side is as KDM noted is that an experienced burglar will eventually be able to see which numbers have the most wear and tear, so if it's a 4 digit code, the crook only has to see which four numbers are worn to make guessing an easier task. The way to prevent uneven wearing of the digits which I have NOT seen is to issue a separate 4 digit code to every person who you want to have access (you can have several active codes on the electric versions). That way you can use all the numbers on the keypad and they each get some wear. Or, you can just change your code every year, or so.
Next bad thing about the electric version is that they require a 9V battery. When the battery goes dead...you can figure that one out for yourself. So I have my keypads on the same replacement schedule as I do my fire/smoke detectors. That is once a year. Standard 9V batteries don't do so well in the cold, so I use lithium, but the manufacturer says to not use lithium because they don't give any warning before going bad, like a standard 9V does. Mehh, hasn't been a problem so long as I replace them annually, I had one go almost two years before the battery went out.
The other thing is to decide if you want the deadbolt to be the combination, or the door handle itself. I prefer the door lock over the deadbolt. The deadbolt seems to be a bit more finicky for the kids to operate than the electric door lock.
For the house, I recommend electric pads. For external shops, I would go with mechanical.
The above doesn't help with you determining which door to put it on, personally...I'd suggest the one you use the most. But, it may help you choose which style you want to use.
