Arcade. Raging Thunder 2. It's just fun. Graphics and speed are big pluses as well. A close second is GT Academy. I like the challenge. I can't win a single race, but I play with the racing line guides off. You know, I want to try win without them.
NFS Shift. Best Racing Graphics, nice mix between sim&arcade, cool sound & ambient. After the update of GT-Racing i decided to purchase it, well, didn't regret it, big amount of content, multiplayer, statistics, etc. but the graphics and some annoying bugs are really making this game feel a little bad. Even in Asphalt 5 the graphics looked better, not only the models of the cars, also the tracks, they look so "Aliased", more then any other racer i have from gameloft. But it's still fun to play, but need to watch out not go get eye cancer For racing-fans it's good to have both and hope for a good update for gt-racing.