It would be difficult. I'm quite sure Revan has smaller, weaker ships. And his ground tactics must have included Dark Jedi, probably as field commanders and elite soldiers. Thrawn, on the other hand, didn't really incoporate most Dark jedi into his tactics, seeing as though there were only maybe 100 DJ in the Empire's reign (in contrast to thousands in Revan's Empire).
I thought it was pretty clear Thrawn > Ackbar.
And I think Thrawn was stated by the narrator to be the greatest tactician ever. Haven't read Heir in a long time though, so don't quote me on this.
Grievous's main problem was he was too sadistic and went too far in needless cruelty. For tacticians, Thrawn, Ackbar and Revan are very high up, no doubt...Wedge Antilles was no slouch himself with the X-wing campaign and General Hoth managed to destroy Sith control over the galaxy with only a few planets' worth of strength to start out.