Most of the akatsuki deaths were just sell jobs, Kishi just wrote them out the story because he couldn't deal with them otherwise.
Sasori - A solid Kage level threat, struggling against early post skip Sakura? I guess his death was alright, what it took to get there was pretty bogus.
Kakuzu - One of the most experienced shinobis ever, survived through multiple eras, even outsmarted Shikamaru at times, falls for a 5 IQ braindead Naruto tactic?
Nagato - TnJ'd despite having conviction strong enough to murder the sensei the TnJ was about in the first place.
Konan - All of a sudden she has morals after Naruto's TnJ, but when Jiraiya (the only adult who ever cared for her) was right there in her face she didn't even have an iota of hesitation/care to spare. I guess this is less a complaint about her death more on her character being completely shallow.
Deidara sold as well, but it was still cool ngl, atleast it went with his motto. Hidan's "death" was a great moment for Shikamaru, and a great wrap up to the arc, but it requires a level of suspension of disbelief to read Shikamaru dodging and placing a small drop of blood on Hidan's spear at full speed with pin point precision, without him noticing, the same guy who was pressuring and keeping up with Kakashi in CQC. Itachi's was great, no complaints there (his first one atleast). Kisame's was cool, but at that point he was nothing more than an irrelevant sideshow, so it didn't have the impact it would otherwise. By the time Obito died, Akatsuki is the last thing I would link him with, he's closer to being a Hokage than an Akatsuki member. As for Zetsu, who gaf it's Zetsu.
So yea the answer is Itachi, by a wide margin.