I don't own either...but I practically live at my LHS which does primarily off-road stuff. I'm like a free employee (but I do get great deals
If you're talking the original T-Maxx...they're fun to bash around with, but they're money pits. You will literally be keeping your local Traxxas dealer in business.
The REVO seems to be quite a bit more capable and a bit tougher, but I don't really have enough experience with them yet.
The Savage can be purchased as a semi-complete kit, so you can buy it and "do it up" with some good servos and a decent radio right from the start...plus, it's a lot tougher than the T-Maxx and they handle better.
You're going to screw stuff up with any of them...but with the Savage, you won't be as likely to break big stuff that's a pain to change, like bulkheads.
My vote...Savage SS-25 kit, an MX-3 radio and couple decent servos. Spend the money up front and you'll get a MUCH better truck.
If he's just a basher, and pretty responsible with his stuff (Not:"I wonder what will happen if I jump off the roof?"), then the T-Maxx is pretty fun, but they do break pretty easily when pushed hard.