If I could only get one I would go for Mario Kart. I love realistic racing games, but Mario Kart is just so much wacky fun that I would miss it more than the other games.
Oh god, I can't really choose. I like both Gran Turismo & Forza Motorsport and it would be seriously difficult if I had to choose just one of them. I'm leaning on Forza Motorsport because of the way you can customize your car with different paint schemes and for that I would be able to spend hours in on there perfecting my "art". But I know if I chose Forza I would at some point miss the weather and time and day changes of Gran Turismo. Tough choice!
This one is really tough to think about. I think that if I had the option and that I could only choose one I think that I would go with Need for Speed. To me I will always think that this is one of the best racing game franchises that is out there right now.
It be rally car racing for the original Xbox. It was a fun game that had so much replay value. There was even a ghost challenge where you would challenge the creators of the game. Their cars would be a faint view of it, looked like a phantom.
I could see why this would be your choice even if you favor realistic racing games because games like MK tend to have more replay value since there are a few more mechanics than just finishing first whereas regular racing games might prove to be a bit repetitive after a while.
I think GTA shouldn't count for this discussion, since it's really a sandbox game and not really just a racing game. It's not fair to include it, in my opinion. Regardless, it's hard for me to choose between Sonic & Sega All-Stars Racing Transformed and Blur. Sega Transformed is probably my favorite racing game because it feels like a much more balanced and faster Mario Kart, and the way race tracks change is awesome, plus you also have the boat and plane sections. Blur is kind of a beautiful combination of karting games and simulation racers, though...
Does Grand Theft Auto count? Because if I could only have one it would be GTA. And if GTA doesn't count as a racing game, then Midnight Club is my second choice. I have a ridiculous amount of fun in my old Midnight Club games just pushing other cars into gas station pumps and making them explode and wipe out nearby pedestrians.
I don't think GTA counts but to be fair I'd love to see them make a racing game that has GTA elements in it. I'm sure Rockstar would do a great job if they ended up making a racing game.