Tough call. Both got stopped in '08 (Sartison by the better fighter at the time, as proven h2h) and both have had a good couple of years since (Stieglitz probably beating the better competition).
As for styles - I think Stieglitz will be more comfortable in a war, while Sartison prefers more of a finesse game from mid-range (and has opted to spoil with footwork and strategic clinching against weaker foes than Stieglitz).
Sartison probably has the better one-shot hand speed, but isn't combination crazy. Combos are the key to beating Stieglitz. I've got Stieglitz pressing the action, imposing his size and winning by decision - or maybe scoring a stoppage in the championship rounds.