New Car sounds pretty broad, and likely pit you against a bunch of Mustangs, Challengers and Camaros. Though reading the list they have their own category, so not sure what would be the other common competitors in the category.
Tuner is going to likely be a zillion Civics and STI's. Both of which are more likely to be reasonably modified, which my guess is that's something the judges would be looking for in the category.
Based on that speculation alone I'd be tempted to enter in New Car. But that's just me rationalizing it in my head with less than one cup of coffee this morning so take it for what it's worth
