This entire battle henges entirely on Sasori landing a single strike on Deidara. Sasori's poison causes paralysis which will greatly hinder Deidara's ability to mold chakra. If he can't mold chakra then his explosions (including the C0) won't work.
The big thing here is that these two know each other WELL. At first glance that would favor Deidara since he knows Sasori's weakness, but let's examine it for a second. This would also mean that Sasori is aware of Deidara's different clay models and how each works (even Tobi was aware of his dragon). Further the databook gives Sasori more intelligence than Deidara (5 and 4.5 respectively), so I'm betting Sasori could use the knowledge that Deidara knows his weakness to his advantage.
Beyond that (and this point has already been made) Deidara did say Sasori was stronger. As hyuzhina pointed out, the wiki says that this may have only been outwordly. However, we need to take into account that the wiki isn't always absolute fact, and it is more of the opinion of whoever the admins are. But it seems to me that Deidara is not one to hand out compliments if he doesn't believe it to be true.
Regardless, unless Deidara uses a massive bomb immediately that will severely damage them both, I have to give the edge to Sasori.
not fair
