Aiko Akura
I'd have to say the Rurouni Kenshin Hero's and Foes. Just because if they have Himura Kenshin, Hajime Saito, Seijuro Hiko, Makoto Shishio (If he is still alive. Lol.), and Shinomori Aoshi (if he hasn't given up fighting yet.), they would basically be unstoppable in a battle (I should also add that If they work together. Heh.) I Don't think the Naruto heros and foes would really have a chance.
Another Understatement of the year....
"Naruto and his friends and foes wouldn't really have a chance against Kenshin and his friends and foes"
Naruto still has the supernatural techniques of Ninjutsu. While Kenshin and them are all very skilled, when it comes down to it, they would really have a hard time with the various Ninjutsus that Naruto and his gang have. The combos the Naruto gang could come up with are infinite.
Zabuza could use the hidden mist technique, then strike out of nowhere. His specialty.
Gaara=Desert Coffin. No questions asked.
Haku-Ice mirrors. Even Kenshin would have trouble dodging his attacks when he uses that skill.
ShikaInoCho combo. Although this one is probably not as good as the others, I'm sure Chouji's Meat Tank could get some people from Kenshin's group.
Hinata's Gentle Fist and Neji's Byakaguran (sp?). Just like Sasuke, Itachi, and Kakashi's Sharigan.