Re: 1998-1999 Explorer or Mountaineer for first car?
As mentioned, either one will work fine. Explorer might be less on insurance than the Mountaineer, it's something to look into as the Mercury is more of an 'upscale' SUV, so to say. I'm not positive that it is higher, but it'd be one of the first things I'd check into.
If I'm not mistaken there were two versions of the V6, a 150hp unit and a 205hp unit, both 4.0L. I can't recall if the OHV or the OHC was the 205hp unit, but the 205 unit is more efficient at moving around 2+tons of SUV and you'll be able to better keep up with traffic once you add the larger rims, some older friends, and a couple of beer kegs in the back!
Parts are also widely available, and are reasonably priced. Your mom lucked out in getting an '09, as the Explorer will go to a uni-body platform in 2010 or early 2011 to keep up with the times.... It's a shame really, but I can see Fords case with that one.
For reliability, same goes for any vehicle here; keep up with the scheduled maintenance and you'll easily get 200K out of the vehicle before any major problems. A lot of people overlook basic fluid changes, more so, in the axles, transfercase, coolant and brake & power steering fluid. If you can't get the previous maintenance records of the vehicle you want to buy, be sure to spend a few hundred bucks and get all the fluids changed out. It'll be one of the better investments you'll make on the vehicle for the long term.
'00 Durango R/T 360ci 290hp (modded); 138,500m
'06 Pontiac G6 GT 3.5L 220hp; 44,000m
'12 Chrysler 200 Limited 3.6L 283hp; 13,000m
'99 Taurus 3.0L 2V Vulcan 145hp; 154,300m - Traded
Amsoil in all vehicles!