[Blackbeard D. Kuma]

^ The Vice Admirals are next in line for a promotion to admiral status, though. They, too, have had years of battle experience and are all proficient with Haki. Moreover, admiral is a rank you really have to work for, and the VAs we know of have more than proven themselves in that regard.

Keep in mind that we have yet to see the full capabilities of the VAs. Perhaps some of them are bordering on admiral level unbeknownst to us. Onigumo, in particular, has this powerful and commanding presence to him. And his feats/missions (sneaking behind Marco and seastone cuffing him; personally picking up Ace from Impel Down) indicate he's no ordinary VA.