Well, it really depends on the brand bought. Coca Cola will clean the rust off of bumpers (well, back in the day when car bumpers were actually made out of metal).
Orange soda will make a frying grill sparkle. Used to use that trick at McDonald's after using their grill soap to get the heavy stuff off first. Seriously, it DOES work. Makes the grill sparkle like it's brand new.
I voted grape soda. Now, I don't know if it's the stickiest, but it sure does stain anything it touches and makes quite a mess.