Hmmm..
1)Igneel's Power - I agree that DF had better feats than IP, but due to hype and portrayal, I put Igneel's Power slightly above.
2)Dragon Force + FDKM - That FDK blow in DF was extremely strong. Feat wise, it's stronger than Igneel's power since it vaporized Zeref's body. However this combination completely drains Natsu.
3)Flames of Savage Emotion - I know people will vote for FSE, and I can understand - the salt is still real. I, however, will move past this salt and give this "form" an honest rating. I think it's number 3, because while it "burned through time", it didn't completely vaporize/kill Zeref. It only hurt him enough for Mavis to talk with him. It is however the most haxy power Natsu has, since at this point, it can burn any almost any hax out there.
4)FDKM/DF - I put these two powerups on the same tier. DF by itself is definetly a lot lower than the combination of DF and FDKM. We don't have any feats to know where DF by itself lies, but I think it should be on par with his FDKM. DF boosts his stats and can burn off magic, while FDKM provides incredible strength and destructiveness.
5)Partial E.N.D Natsu - I actually think it was impressive. For a partial transformation that is. Too bad we won't get the real deal
6)LFDM - We can't really rate it since it hasn't even been used once post-timeskip, but I doubt it's relevant anymore. Hell, if it would be relevant, Natsu would actually use it.