-Mace Windu vs Dooku. Two old friends and apparently two of the best duelers in the jedi. Would have been cool.
-Obi-Wan vs Palpatine. Palpatine would have kicked Obi-Wan's ass but still wish it happened. Obi-Wan and Palpatine never really interact much, and Palpatine probably hates Obi-Wan a lot for always getting in the way.
-Anaken vs Mace. They constantly butted heads and I really thought it would happen. Both were very similar to each other, having amazing power and also at least somewhat using the dark side during fights.
I think for me it'd be Dooku vs Sidious. The guy held his own against Yoda without breaking a sweat, surely he would give Sidious a good fight, and perhaps even be capable of defeating him.
Another I'd have liked to see would be Obi-Wan + Anakin vs Darth Maul. Get rid of Dooku in ep. 2 (and maybe even ep. 3) and replace him (and Grievous) with Maul.
I know Obi-Wan defeated Maul in ep. 1 but, his death never really made sense to me. He pretty easily held his own against Obi-Wan and Qui-gon, kills Qui Gon, and then is beaten 1v1 by a low level Knight. I don't care what amount of anger Obi-Wan mustered to fuel his ability, he should not have beaten Maul. Maul should have wiped the floor with him, and be forced to retreat just before killing him due to some environmental hazard or something, where his character can be developed further in ep. 2. Then, in ep. 2 or even as far as 3, a much more experienced Obi-Wan (+ Anakin) faces off against Maul once more. Maul disables Anakin easily but Obi-Wan is strong enough this time to put an end to Maul. Things would have made much more logical sense if they'd played out this way, imo.
Yes. If we're talking episode 2 and replacing Dooku with Maul, Anakin rushes in like an idiot and gets put back on the bench. If Maul survives to episode 3 (replacing Dooku again), then it wouldn't make sense for Anakin to defeat him, not necessarily due to lack of skill but just because story-wise, Obi-Wan should be the one to avenge Qui-Gon's death by killing Maul.