Saying he's on admiral level is frankly retarded, even vice admiral level is a little out there. You guys are underrating the admirals and overrating luffy. Some of the strongest pirates in the new world practically pissed themselves just at the site of akaino, even blackbeard fled at the site of him with all those powerful allies who it's safe to say were probably as strong as luffy is now. He's definitely on shibukai(spelling) level, the only thing is you can't really classify shibukai as a level, since it seems they're all on different power levels.
Moria, was quite pathetic at his end, it seemed he couldn't even scratch doflamingo.
Crocodile, seems to be pretty strong, but a very obvious and exploitable weakness.
Hancock, seems to be extremely powerful, not quite the big 2 shibukai but still really strong.
Jinbei, Same as hancock.
Puma, before his cyborg upgrades I'd say he was level with jinbei, after them(even though he's been wiped) I'd have to give him an edge.
Hawkeyes/doflamingo, They seem to be on a "diffefrent level" more like admiral and emperor level, just but their act around emperors and admirals, they seem even more cocky than the others.
I'd say luffy is a little under vice admiral level, even though he'd put up a good fight against an admiral because of his haki usage, as displayed in recent chapters it still isn't all powerful, just because he can hit them with haki doesn't necessarily mean he can do a considerable amount of damage, even without their DF I'm sure the admirals are powerful, so even if he could hit them doesn't mean much, gives him a much better chance but doesn't mean much.