Rassie, its obvious imo. Thats why they brought him in a few months ago. IE: simple gradual transfer of the reigns. Heyneke is I reckon is focused on the bulls and still has a bit of a stiff lip from losing out 4 years ago. Alistair is 2cm away from being ready. If he can nail a currie cup or S15 then he's ready.
Rassie has not nailed a S15 but is responsible for pulling the cheetahs right since 2005 when he got involved. Indirectly I believe the Stormers resurgence these last 3 years has alot to do with his input as well.
Besides Rassie is tacticly so slimy not even the sea could wash him clean.
If he only knew his time to have gone was 2 years ago already.
My vote goes for Heyneke. Took the Bulls from Super rugby wooden spooners to champions. He has the big match temperament and know what to say at finals, halftime in change rooms. He also excellent at spotting talent.