They are all incorrect because you must use NICER, not nice. With NICER, all of them are correct. "...than I do" is best for writing and "...than me" is best for speaking but not OK in writing. "...than I" is correct, but nobody talks like this-- it sounds uptight and pedantic. Actually, though, the best way to say it is: His car is nicer than mine.

He has a nicer car than I do. ( This is correct, I am a Native English Speaker) Although this is said in spoken English "nicer" may or may not be a real word ,now that I think about it.

You know what? Check this out: http://grammar.quickanddirtytips.com/than-I-versus-than-me.aspx

None of them are correct. You have to use "niceR".

the last one .