Right now I am playing Association mode, with the Shawn Kemp Sonics team from the "all-90's roster" included in the Ultimate Base Roster Patch! Usually what I do is I just play 1 season (the reason why I like Association is because of team chemistry and team roles), and then start another season with a different team, perhaps in a different era. I've never played more than one season in any 2K game, so I wouldn't really know how the draft classes for rookies work, I think they auto-generate them.. I can imagine that creating them from scratch would take forever!!
I've also tried MyCareer a few times, might give it a go once again that I have the classic rosters.