Just retire Akaar already. Do we need to have a head of SF character, during the TV series they just tended to trot out an admiral when they needed a bit of top brass action
There are two canon heads of Starfleet: Admiral Morrow from TSFS and Admiral Bill from TUC. Personally, I was annoyed we never found out who held the position at all in the 24th century.
I thought Fleet Admiral Shanthi (seen in "Redemption, Part II" and mentioned in "The Pegasus") was supposed to be the head of Starfleet? http://en.memory-alpha.org/wiki/Shanthi
There's nothing indicating for sure she was, even that Memory Alpha page just says she was a senior officer with Starfleet Command. I suppose the title "Fleet Admiral" kind of implies she was, isn't Fleet Admiral Akaar's title? But then, she only has the pips of a Vice Admiral, and head of Starfleet should be a full Admiral.
This has me wondering, what about Leyton? One would think he'd be the head of Starfleet is he was trying to stage a coup, otherwise any officers who outrank him might have some serious objections to him taking control of the government. But then he too was only a Vice Admiral.