Overdriven knows what he's talking about.
First choice would be a Losi XXL, as IMVHO it really is the best nitro MT available. By far the best engine available in an RTR. Even the pipe and clutch are good and if they ever need to be replaced, just get stock ones cheap on ebay. The XXL is pricey up front, but in my experience ebay chop shops make them very cheap to maintain. The tires last forever(OK, the XXL rims are ugly IMO..) The radio is perceived by many to be good for an RTR(not a big Spektrum fan, but hey.. I'd sell the radio if it were me and recoup some dough..) The XXL is VERY fast for an MT, and handles great. Losis are very tough too. As stated, all you really need is an off-brand engine brace. After that there are a few other things that can be upgraded over time. I tend to disagree that the BAC link is "necessary", but people seem to like them. I've never had problems with the stock link, and my first LST2 (same as XXL basically, just shorter chassis) is six years old, my second four.
A New Era rollbar is very nice - if you can find one. And after that, you can get things like a wing kit, different shock springs, etc.
If you don't go with the Losi, I would have the Savage X4.6 next on the list. I personally don't think HPI quality is what it used to be, but basically the Savage should be an alright first nitro basher truck.
I would never buy another thing from Traxxas. IMO the Traxxas business philosophy is to sell shiny, appealing looking and overpriced RTR's with fantasy-land speed claims, which in reality need lots of upgrades to be made durable. I can well imagine a Revo with the "necessary" mods will cost more than a Losi XXL. And the XXL would run over it. But hey, some people like Traxxas, and insist on believing the phallacy that you have to rely on your local Hobby King chain shop that pushes Traxxas (and all the necessary mods for them)
Anyway, XXL, and failing that, Savage X4.6.