basically who would natsu tie up with in a fight one on one no nakama power up just his power alone? please say why.
(besides anyone in the series)
Gajeel is the obvious answer. Natsu had his second origin unlocked and Gajeel trained for however many weeks straight, which made them seem about equal during the Grand Magic Games. Natsu just had to steal the glory by sending Gajeel rolling away in a mine cart. They both have a secondary dragon element now, too. I hope they have another showdown at some point.
Other than that, I want to say Gray, but he doesn't seem to be keeping up. Maybe he'll get a power-up of some kind soon (considering what's going on in the manga right now, that's definitely a possibility).
If we're not restricted to Fairy Tail characters then, I dunno, Krillin maybe? Yes I'm being serious, Krillin's only weak compared to the guys he hangs around with! He's a pretty tough dude!
Moving this thread, it's a very specific topic so it doesn't belong in general discussion.