User blog comment:LegerPrime/Natsu vs. Acnologia/@comment-74.127.135.27-20151019133554

Honestly, IDK if he would win. Just an FYI, I'm not really a big manga reader so correct me if I am wrong, please. Think about it this way Since Acnologia apparently used more force on Gildarts alone then the rest of FT, I would say in if Acnologia was in Dragon Form, Natsu wouldn't stand a chance.
 * We know that Natsu, while he has grown in power, was not able to beat Gildarts, though he had improved before he went training for a year. So we can assume that his power has increased considerably, though it's still in question whether he could win against Gildarts. (And we can also assume Gildarts has been training as well.) Since it hasn't been proven otherwise I'm just going to say that Gildarts is still probably the strongest in FT.

I'm not really sure about Acnologia as a human. It would definitely be interesting to see the matchup, but since I'm not totally up-to-date with manga I won't really say much more on this one. I'm sure Natsu might be able to hold his own - at least in DF - for a bit.

Of course, if he was really desperate it's possible he might do something w/ his right arm, but I doubt he would use a weapon meant to be used against Zeref against Acnologia.

Just my opinion!