User blog comment:D.Dragon123/Ranks status/@comment-5729687-20130106084646

I think it is also depends on the location of the marine and not just the rank. You could say that marines from East Blue are the weakest except Smoker and Tashigi. I'm pretty sure that Coby and Helmeppo in pre-time can beat someone like Captain Morgan and Lieutenant Fullbody because Coby and Helmeppo are more of a Grandline Marine, which deals with stronger pirates than someone like Captain Morgan, which only deals with the weaker pirates in East Blue.

About Rank, well it somehow a good indication but not the best indication. Strongest people in the marine has the rank of Admiral. Fleet Admiral is basically an admiral with more authority, they are for most part on par with an admiral so you can say that Akainu is still on par with Kizaru unless otherwise it is said in the story on who is stronger.

In Luffy's case, he might be able to beat a vice-admiral but not easily, so it will be like when he is fighting Lucci, Luffy might win but with a desperation attack like Jet/Elephant gatling gun, with luffy almost dying.

The highest rank that Luffy beaten so far is a Vice-Admiral, which is Garp, his grandfather, and it is because Garp pretty much just let Luffy pass.