Well, I am a Losi fan when it comes to MT's. The Aftershock has some flaws - thin arms, 14mm hubs, a bushing instead of a bearing in the 2-speed, and a crap pipe for ex..(All of which is remedied with the XXL of course..) That said, it will be a BIG truck for an 8th scale, and will be fast and handle great. For general bashing around the yard it will be tough enough.
I personally do not like Traxxas because IMO their modus operandi is to sell shiny, nice looking RTR RC's that are actually pretty flimsy, and need lots of hop-ups to be reasonably durable - which is how they really make their money..
So between those two I would get the Aftershock.
But again, without in any way trying to talk trash or argue or anything like that, based on what you say you want to do, I kind of think the Savage X 4.6 would be a better call. I would expect it to be a bit more reliable and tough than the Aftershock.. Depends of course on how you treat it...
Generally, IMPO, my top-3 list of 8th scale nitro MT's would look something like this:
1.) Losi XXL - the "Cadillac" of MT's. Or Porsche, if you like...*
2.) Savage X 4.6. Good, fast, solid RC.
3.) Savage XL. It would be #2, but the engine has a terrible reputation. With an LRP .30, switch it up to #2.
The Aftershock would be a few notches below those, and any Traxxas further below that.
But OK, you gave your options, so that being the case, Aftershock...
* I assume your reason for excluding the XXL is price. And I understand that. The point I would lay out for you though is the following: RC is not an activity to think about doing over the period of say, a week, or even a month.., but rather over more like a year(maybe more..) Once the gallons and months start going by, stuff will wear out, and possibly break depending on what you do. In the case of the Aftershock, you will be looking at upgrading to XXL stuff as you go.. - because basically it's dirt cheap on ebay chop shops, and you might as well if the stuff is beefier than what's on the AS. But, to really convert, you need A LOT of stuff. The XXL is really beefier - in a lot of areas - hubs, carriers, shafts, drive-cups, etc.. Not to mention more or less "needing" new XXL stuff like the HD pipe right off the bat if you get an AS(OK OK you don't absolutely NEED it - but most would tell you to do it because it will make a big difference - which it will... Plenty of guys been through the last years reporting precisely that...)
In any event, you have your reasons, so that's fine. IMO get the AS, and an XXL pipe off jennysrcparts on ebay.com to get started. As time goes by, get an alu clutch out of an XXL, and eventually maybe also a 2-speed(I've bought several of each over the years from jennys...)
ps Check prices for Losi stuff at www.overdriverc.com
.. He normally has the best prices on Losi kits that I know of..