No Prep Time
Setting The hidden leave
Each at full power
Pain still wins, Sasuke isn't that strong yet. From what we've seen so far Itachi was pretty much equal, if not stronger than current Sasuke, and I have always ranked Pain as being slightly above Itachi.
Sasuke gives him a very good fight but goes down in the end, if it comes to it he has nothing to stop Chibaku tensei.
i think sasuke might pull a win if he uses tsukuyomi. also he can spam amaterasu arrows which would kill pein rather easily, also most of pein justsus take considerable time to get going. sasuke might not have the destructive power of pein but his attacks are far faster, not to mention peins prime weakness is genjutsu
@othus12: Pein's prime weakness isn't genjutsu. The genjutsu that Jiraiya used was a very high level genjutsu, probably the most highest level genjutsu seen in the entire series so far that takes a fair amount of prep time and requires the use of two extra people. Also you forget that Rinnegan is superior to the Sharingan and Sharingan techniques probably won't be as effective, even Sasuke was able to overcome Itachi's Tsukiyomi without the use of MS. Also Sasuke isn't as proficient in using Tsukiyomi as Itachi was, as mentioned by Danzo. So I highly doubt Tsukiyomi would be effective in this fight.
Pein can absorb all chakra, as he has shown several times and can see everything the other Peins see so I don't see how Sasuke could hope to land an attack. I also highly doubt Pein would just be standing there waiting for Sasuke to spam his attacks so if this is the 6 paths of Pein here, Sasuke can expect to be attacked from 6 different directions at once. Sasuke's not a very fast ninja at all, not compared to the likes of Raikage, SM Naruto or any form of current Naruto or Minato. Speed wise he's probably slightly superior to Kakashi from his feats shown, which doesn't mean he's slow by any means but he can't compete with the top 3. So in this fight he wouldn't have the same advantage that SM Naruto or SM Jiraiya had of speed. If it's not the 6 paths of Pein, then Pein has an even bigger advantage because he can just absorb everything Sasuke throws at him and then use Shinra Tensei techniques to deal with him.
Sharingan<Rinnegan. This has been said several times, even Madara's Sharingan evolved into the Rinnegan. Sasuke<Pein. Maybe if this was Itachi we could've had a fight on our hands but it's not.