I must agree, this fight was rather impressive. It's a pity Quin-Gon didn't get to show off his Ataru techniques. I'd have liked to see that Form used by someone other than Yoda.

Not true. Though he was the only Lord the films show, there's always more than one Sith Lord. There's no possible way Sidious can so easily be considered the most powerful of that time.

This is a terrible assumption. The Force offers various abilities for both Jedi and Sith to harness, and Yoda's Force Absorption is of the strongest defensive abilities. He does not "bounce back" the Lightning, but attempts to absorbs it; failing.
As for stopping the senator stands, note that Sidious was hurling multiple stands at Yoda. He will not concentrate all his force onto a single one at any time, will he? So it's only expected that Yoda would've been able to send it back. T'was cool though.

But if we're going to deliberate who's more powerful out of the two... explain how Sidious never seemed to tire. Explain why Yoda was so utterly exhausted.

Yoda is considered the most powerful because of the fact he's lived nigh-on a millennia to utilize his abilities. Placing bets, I'd say Mace would have a pretty good chance of teaching Yoda a thing or two. In all honesty, I doubt there's a most powerful at all; the Forms used all have weaknesses, and another Jedi/Sith could have the counter-Form within use. Just depends who's fighting who at the time, really.

Of the originals, this was also m personal favourite. The dramatic impact the fight had was incredible. I'm a sucker for flashy fight scenes though, so my vote will always be within the newer trilogy.

Yoda v Dooku

It was just fantastic seeing Yoda in a lightsaber duel, easily the highlight of Attack of the Clones. Anakin v Obi-Wan had a nice intensity to it though, and Obi Wan's rage and sadness at the end of it was a good touch.