General Grievous vs Mace Windu:
This would be cool. Grievous is a formiddable opponent due to his combination of speed, reflexes, strength and tactical mind. I believe he was trained in swordsmanship by Dooku. He has defeated five Jedi at once.
Mace could still win this one, with his swordsmanship, experience and Force touch, although it would be by no means easy. His Form 7 style of fighting could also be a good equalizer. He might be able to win by dropping something very heavy on Grievous's head or by Force-pushing him over a huge drop etc. All in all, it could go either way.
Mara Jade vs Darth Maul
This would also be good. Both were abducted at a young age and trained by Palpatine. I think Maul has the edge in combat ability, although Mara is a highly skilled swordsman in her own right. However, I think she'd win this one as she has more personality and will of her own. Mara would be able to adapt to changing situations more quickly than Maul.
Free for all! Throw em all in there... screw it...
That would just be sick.
But if I had to have a request, it would be an honest battle between Obi Wan and his apprentice. Not the old farts jabbing and poking at each other as we get to see, but an all out battle between the both of them in their prime. That would not only be amazing, but it'd be closure.