as long as sasuke isn't there to get caught up in the destruction, my money is on itachi beating the shit out of deidara regardless of his "method" to get out of sharingan genjutsus since itachi has so much more than just that.
we never saw itachi do anything except hold back against sasuke twice, hold back against deidara (akatsuki was recruiting/testing him so death was out of the question), and his clone was weaker than the real thing but still it held back in kanohagakure. imo itachi's fighting ability unrestrained puts him at the top of the naruto ranks, he's up there with the sannin and shit.
Originally posted by Csdabest
Technically HE CAN beat pain. Dei trained to fight and kill Dei so he has some defense against Itachi Genjutsu which is his main weapon.
you forget itachi is as fast or maybe even faster than his brother. Deidara had some defense against sasuke's genjutsu but look where that got him and that wa before he got the MS