It depends on the matchups. For example, against the Heat during the playoffs last season, Bass was too slow to keep up with Lebron when the Heat put LBJ at PF. Of course, no one can really stop Lebron, but Green would have been a much better matchup.
Against the sixers this year, if they play Bynum at center and Hawes at PF, Bass would be the better matchup.
Still, I believe you should always play your best 5 guys, and Green is definitely the better player.