Ok so here's my current deep thought....
Yoda tells Obi-Wan he is not strong enough to face the Emperor, but I think Obi-Wan is the strongest of the Jedi (movie era)

Here's why....

1) He defeated Darth Maul
Yes, he had Qui-Gon's help, but Qui-Gon perished. I think perhaps Qui-Gon may have sacrificed himself to let Anakin be trained by Obi-Wan, a "much wiser man" than himself. It seems to be that two Jedi vs. one Sith are not a good idea. Maybe the Jedi are too concerned about hurting each other and they don't fight very effectively.
2) He lived through Order 66
Yes, he did get lucky that the cannon blast wasn't fatal, but he outwitted his troops, search droids, and snuck himself back safely

3) He took on General Grievous by himself and won
The Clone Wars cartoons clearly show Grievous' dominating every Jedi he took on. Ki Adi Mundi, Ayla, and Shak Ti all failed together agianst him. he decimated many Jedi, and Obi-Wan fought him fist to mechanical fist and lived to tell about it.

4) He took on Darth Vader by himself and won (the first time)
Anakin has a higher midi-cholorian count than Yoda. Anakin was full of anger and dark side power, yet Obi-Wan defeated him fair and square.

Obi-Wan therefore defeated two Sith apprentices

Now you may be saying "but Pete, he didin't beat Dooku either time he faced him." True...here is my rebuttle:
the first time he faced Dooku, he had just spent perhaps more than a day being held hostage, he just fought a major battle against droids and Acklay and he was clearly exhausted, whereas Dooku was well rested. Also, he was worried about Anakin messing things up, so his focus was off (again, two Jedi against a Sith is not a good combo).
The second time, he was thrown by Dooku and knocked unconsious. this is because the Emperor was using the Force against him, and he was outduped.
"He didn't beat Jango either..." Although Jango is CLEARLY the coolest, methinks had Obi-Wan faced him again, he would have taken him out. Jango has plenty of tricks, but without a chance to run away, he would eventually be defeated. He should have defeated Jango in the arena, not WIndu.
Despite these arguments, I think Obi-Wan was strong enough to face the Emperor, but that kust isn't how it panned out. I was going to suggest that Obi and Yoda should have taken them one at a time together, but the prrof is in the pudding that Jedi suck at team fighting. Not just my above examples, but remember Kit Fisto and friends dying without much of a fight against Sidious...man that was pathetic...