Argh dammit. It would've actually been more interesting if Sengoku was out and it was between Rayleigh, Aokiji and Zoro.
Rayleigh is getting old and he did indirectly suggest on SA when he was fighting Kizaru that he wish he could've helped the SH's at the same as fighting an admiral. Ok, maybe he didn't say that but I got the impression he was indicating to something like that. I think out of all the "old generation" of Pirate and Marine legends we've been introduced to so far; Rayleigh is the most dangerous of them all. He's probably got the best haki around and he can effortlessly take out many soldiers/pirates without much trouble. He has a lot of experience over the years and will be quite a difficult fighter to break down.
Sengoku is similar to Rayleigh in the sense that he too has a lot of experience, is recognised as a key asset of the marines and very powerful. His devil fruit ability is one of a kind which I still have doubts on tbh but it's clear he can KO some of the most dangerous criminals around with ease. It's actually embarassing that he didn't continue pursuing or taking care of the Blackbeard Pirates during the end of the Marineford War. He should've taken care of them while the admirals focused on WB & co. Oh well.
Aokiji has a pretty cool devil fruit ability and he obviously is a good haki user. We've seen him countless times against various opponents mainly during the Marineford War arc and he definitely seems to be the type to have a lot of stamina. Fighting stamina if there is such a thing. So I reckon he could hold his own against the other two. However, I would still consider Sengoku and Rayleigh too much of a burden for him. Kizaru had his work cut out for him against Rayleigh on SA and that admiral has been around far longer than Aokiji. I think Aokiji has still much to learn and Rayleigh would defeat him in this instance.
I vote for Sengoku and Rayleigh.