General Grievous vs. Darth Vader (OT)
This is Vader in his prime during the OT vs. General Grievous in EU. Personally I think that Grievous would win. Vader's chance of wining is using the Force. I think that Grievous will be able to dodge Vader's Force attacks and once he engages Vader in saber combat he's won cause there's no way Vader's going to be able to block all of Grievous's sabers at the same time seeing as how fast Grievous moves them. I mean, EU Grievous put up a good fight against Mace Windu (LOE), defeated 5 Jedi on Hypori pretty easily (two of which were Council members, though they were all tired this is still a great feat), defeated 4 Jedi Masters with easy in LOE before kidnapping Palpatine and survived a huge explosion at the end of the General Grievous comics. So I'd say he has Vader.