1. DF Natsu
2. Dragon Irene
3. Human Irene
4. Laxus
5. FDKM Natsu
6. DF Gajeel
7. God Serena
8. WSDM Sting
9. Base Natsu
10. Base Gajeel
11. DF Wendy
12. Base Sting
13. Rogue
14. Base Wendy
15. Cobra
Well I got time to kill, so why not do a rather extensive write-up:
1. DF Natsu
This should be pretty self-explanatory. Natsu was able to vaporize Zeref's body into nothingness. In all 540 chapters of this manga we have literally never seen anyone else do that to ANY other mage, let alone someone of Zeref's caliber.
2. Dragon Irene
Broke all of Erza's bones in a single swipe and summoned a meteor from freaking outer space. She'd probably still be alive and kicking ass right now if she hadn't had the misfortune of going up against one of the most PoF asspull characters in all of existence.
3. Human Irene
Would have beat the shit out of both Erza and Wendy if it weren't for her pride and stupidity. And her enchantment feats before that were pretty impressive too (though Wendy somehow being able to counter them was pretty lame).
4. Laxus
Scared the crap out of Ajeel with a casual nuke and beat a Spriggan who was immune to his magic while half dead. Granted he did receive an electric charge midway through the fight and he did end up needing to pull bs out of his ass in order to actually win, but his feats beforehand were very impressive nonetheless.
5. FDKM Natsu
Very close to Laxus's level, but just a tiny bit below. He was capable of beating Jacob and evaporating an entire lake with a single attack. And his heat aura was so powerful it hurt Spriggan level opponents just by being in their vicinity.
6. DF Gajeel
Tore a hole through Bradman's body with a single punch, but considering the fact that he's an Etherious whose body was made up of MBP, I'm skeptical of how impressive that feat really was.
7. God Serena
Contrary to popular belief, possessing multiple kinds of magic doesn't automatically make you OP. However, he did stomp the everloving shit out of the GoI, which makes him pretty damn strong (though his opponents were rather featless).
8. WSDM Sting
While he was able to take out Larcade, a top tier Spriggan, keep in mind that new modes have always been shown to be more powerful when they're just acquired and running off of someone's else's MP, compared to having to fuel that mode with his own MP alone. As it stands right now I wouldn't put WSDM Sting without Rogue's MP anywhere above average Spriggan level.
9. Base Natsu
Melted the Domus Flau, evaporated Ajeel's Sand Pit, twoshot a Spriggan (albeit a very physically weak one), oneshot Bluenote, took out hundreds of soldiers with a single roar, etc etc. The list goes on. Though they're not quite top tier feats, they're certainly enough to put him at this high of a level.
10. Base Gajeel
Had some cool feats against fodder soldiers and was able to at least hold his own against a Spriggan he couldn't even touch. Apart from that though he really doesn't have much.
11. DF Wendy
One of the faster mages in the series and capable of dealing at least noticeable damage to Spriggans. Not much else to say.
12. Base Sting
Was able to deal decent amounts of damage to a top tier Spriggan. Didn't really do anything else this arc.
13. Rogue
Capable of at least fighting on par with a Spriggan Historia.
14. Base Wendy
Her enchantments are top-notch and she was even capable of countering Irene's enchantments (though the legitimacy of that feat is uncertain). Leaves a lot to be desired when it comes to direct combat and offensive capabilities.
15. Cobra
Literally been useless this entire arc. Hopefully we'll see some more from him in the upcoming chapters.