MP3 256 VBR or MP3 320 CBR ?

Well, if "you can't really hear the difference" then I guess they are equally good!

It is really a matter of preference, but just to let you know what the retailers are doing: most online music download stores that sell in MP3 format use MP3/256 VBR. The stores who cater to a DJ-oriented audience, who will presumably be blasting their purchases over awesome sound systems, mostly use MP3/320 CBR.

VBR can give slightly better fidelity at a given bit rate, since it uses variable allocation of bits, thereby coding "complex" pieces of the music more accurately. At the higher bit rates as you are talking about, it is not a strong difference.

Feel free to rip a piece of music both ways from a CD, and listen to what (if any) difference you hear when you play them back.

With VBR, can the bit rate exceed the specified rate? i.e. with 256 kbps can the bitrate "vary" above 256, or does the 256 dednote the maximum possible bitrate? Thanks.