like the title says, what two ponies would you most want to go on a roadtrip with? This shouldn't be about your favorite ponies, but rather the ponies that you feel would make the best companions for the trip.
Also, two worst? Again, based not on personal preference, but on how well they would cope with the journey.
Best: Twilight and Applejack. Whilst not my favorite ponies, these two would do incredibly well on a roadtrip for a few reasons. The fact that they are the most level-headed two out of the mane six would mean that important information, like directions, would be able to be relayed for me in precise, no-nonsense ways. At the same time, because they are two of the most stressed ponies on the show, I can imagine that they would appreciate the opportunity to relax and enjoy the trip, regardless of what was planned along the way. Finally, I could imagine that both of them have a little experience tinkering with machinery, so if something went wrong with the car, I'm sure they wouldn't mind lending a hoof, and might even be able to get you back on the road.
Worst: Rainbow Dash and Rarity. This depends a lot on where you are headed, however, because if you were headed to, say, an air show and a succession of high-end boutiques, and doing it in a fairly modern and quick car, I'm sure all would end well. But, me being a car guy, I'm trying to think of a more Hot Rod Powertour-type scenario of taking an old car halfway across the country. An old car that probably doesn't have Air Conditioning, and that would probably break if you pushed it too hard. I think you can probably see where this is going. Rainbow would most likely spend the trip commenting on how slow we're traveling and sleeping. Also, not sure how well she would do having to wait on the planned lunch and dinner stops after seeing her impatience to get lunch in The One Where Pinkie Knows. Rarity, while probably a decent navigator, would get very uncomfortable riding in a hot car witht the windows down staying in low-cost motels, and eating processed red meat and deep fried potato products the whole way. So, whilst they would still probably make it to their destination in good shape, they probably wouldn't enjoy the trip as much. Although, I'd jump at the chance to take any pony on a roadtrip, even these two.
So, how about you guys? Who would you think would do the best, who would do the worst?