It's either soda, soda pop, soft drink, or Coke. I don't call it Coke often (unless it is actually Coca-Cola), but sometimes the redneck in me will show up. > _> I usually just refer to individual drinks by their name or type, but if I'm generalizing, I most often call it soda.
As for favorite flavor, I think I'm going to have to go with grape. There are a lot of great flavors out there, though, and it really depends more on my mood.