For starters I'm taking the best player at each position in league history, but for the bench I will focus more on role players that I could see being ok on the bench on this type of team
Starters - Magic, Jordan, James, Duncan, Kareem
Bench Smalls - Lever, Kerr
Bench Wings - B. Jones, Korver
Bench Bigs - Rodman, C. Robinson, Eaton
I think that 12 man has the right mix of scoring, defense, passing, etc. The right amount of specialists on the bench.