Well I did like the Warthog, I have to admit, but it's not great for the highway I'm guessing. The Mako is an arse to drive so that's out.
I'm going to be true to my petrolhead genes and pick the Imponte Ruiner from GTA4. Ok so it's not the fastest but with a 7.3 litre, it doesn't hang about and it handles bloody well when you get to grips with it. Plus it looks fantastic in black with gold trim!
http://images1.wikia.nocookie.net/__cb20100318181602/es.gta/images/a/a5/Ruiner_GTA_IV.png
Wardy