Hmm let's see. I don't think flash freeze is relevant here. Pre-timeskip, Mard Geer was able to break out of the ice with little difficulty despite being a demon, and Natsu was able to do the same in base. Post-timeskip, Gray has never used flash freeze against anybody other than fodder soldiers, and Ajeel was able to avoid it no problem. I think it's safe to say Gray can't roflstomp freeze anyone spriggan tier and expect them to stay frozen. Range-wise, Gray has more options, but Gajeel has breath attcks/Iron God Sword to contest range. I would imagine this fight to be cqc, since Gajeel has a habit of closing the gap as soon as he can, and this DF form seems to be pretty good at that, looking at how easily Bloodman was rushed down. I think it's also worth noting that Gajeel's raw cqc was what took Bloodman down, rather than a secret art or special attack that took down every other spriggan. I would say if this fight gets to cqc gajeel wins this, but if Gray can keep at arm's reach, he can pelt Gajeel to death. So I think this is a matter of how well can Gray can avoid taking damage. His main ways of avoiding conflict are A) making ice clones and B) putting up ice walls. Ice clones are next to useless against dragon slayers in general, since they have advanced smell, hearing, and tracking abilities. Ice walls might prove to uselful here, since I think Gajeel can cut them down with his God Sword, but they would stall enough time and be troublesome to deal with. If Gray can pelt from range and play keepaway long enough for dragon force to end, then he takes the win, but I see too many scenarios where Gajeel takes this. My vote is for Gajeel, but very close match.