personal preference. do you want a sports coupe or a sport sedan? are you looking for power or luxury?
the TL is a 3.2L, v6 engine that makes about 29mpg/20mpg highway/city, and has 270bhp/238 ft lb.
the 350z is a 3.5L, v6 engine that makes about 26mpg/20mpg highway/city, and has 287bhp/274 ft lb.
the specs line up about the same, i guess it really comes down to if you want to be driving a two door or four door.
i personally like the TL, it offers so much more room