Yea if you want an electric, with Nitro type performance, Brushless is the way to go for sure, its a bit of an expense, but then again this aint a cheap hobby..
The 2 models lord has got there are good, the Losi is very new and as such i dont know much about it and neither do a lot of people, the rustler is a very good starting point with plenty of options for upgrades in the future, and as its designed around the brushless system upgrading is failry straight forward...as with electric's, the performance boils down to the batterys you use, so spending that little extra on batterys does indeed help a great deal.
Also i would suggest at least 2 packs/sets of batterys, so this prolongs the running time a little bit more, ensuring a little cool down period before whacking in the new pack after the other has died.
also check out the MSUK forums, very friendly bunch of guys there, and lots and lots of info on a wide range of models.
Oh and you never said if you wanted on-road - off-road buggy - off road truggy - or a full on off-road truck such as the Savage.