The 1.8 is a turbocharged 4 and the 2.8 is a n/a six. From what I have read the six is only slightly more powerful but not very moddable unless u gop for a supercharger which is muy $$$. The turbo 4 has a lot of parts available for modding and I would guess you may want to mod anything u get at least a little. I have to agree with PiotrC70 and reccomend u get the 1.8t, on top of being more moddable and cheaper it is sportier I believe it comes with black or carbon fiber trim while the 2.8 has wood(not positive on this but almost.) And quattro is the all wheel drive model of the A4 some are just front wheel others have the quattro option. The prices on A4's vary alot because of the different combo's you can get. Also you shouldnt compare this to a five series a A6 would be a better comparison but between the two i would probably wanna get the BMW.