I think Kenobi vs Maul/Opress might be my top 1.
Apart from how cool the fight looked, it was just the sheer excitement of Kenobi being left alone to face both these beasts. And by all odds, he really shouldn't have stood a chance, yet came out victorious.
Not like with Sidious vs the same duo, where the excitement level isn't the same because we know Sidious is by far the most powerful combatant there and the brothers have no chance of victory and they do lose, and it's Sith vs Sith so it's not like the audience is going to be particularly sympathetic to either side anyway.
Not saying Sids vs the Bros wasn't a really cool fight. Of course it was. But in terms of entertainment Kenobi vs The Bros comes on top for me.
This fight is also excellent and totally doesn't make Grievous look like a loser at all. You'd think it would. But you'd be wrong.