Why is Garp here? Lol
Anyway probably Akainu. The admirals generally lack personality but Akainu in Marineford was great, donuting Ace was the cherry on the top. Too bad that after the time skip that menace got chained behind a desk and he can only scream and do mean faces from there now. But the old Akainu in Marinford was very good.
Then about the others... Kizaru is just your average stoner, Aokiji is a good guy but I don't really care from him, let's see what the BB plot will bring, Aramaki is an idiot, Fuji is not even that bad (character and df power) but again I don't really feel him. Garp is not an admiral and Sengoku was even pretty cool with Marineford and the Corazon stuff but now he is basically retired (for good unlike Garp, at least for now).