My rule of thumb:

1-3 : your top 3 OBP, in ascending order of SLG (worst SLG 1st, best SLG 3rd).
4-8/9 : descending order in SLG.  If 2 or 3 guys are fairly close in SLG, then order them by OBP.

Same as everyone else with two small differences.
1) It is my impression that the leadoff man attempts to steal more than anyone else in HBD, so if the team is going to be set at 3 or higher basestealing I give a significant bonus to somebody who can steal effectively here (BR and SPD both >70, or SPD> 90 and BR 60-70).
2) Studies have shown that the #5 hitter leads off an inning more than any other lineup slot except leadoff.  So I give a bonus to higher OBP in the slot.