Here are my votes in order:
1). Mard Geer
Only one spell is needed to explain why he takes the top spot, which is Memento Mori. Memento Mori could easily destroy everyone in this fight. All the participants in this fight have nothing to counter this spell. In other words, Mard Geer comes close to being undefeatable. I'd rank him Spriggan tier without a doubt. We shouldn't forget about Alegria, Thorn Curse and his Etherious form as well, since these are pretty powerful too. One thing is sure, Mard Geer is overpowered.
2). Mirajane
Mirajane has a major advantage in this fight thanks to Seilah Soul. Thanks to Macro, she could control a lot of opponents and easily overpower them. Her Satan Soul has a lot of powerful spells as well, since these have pretty high AoE and don't take a long time to cast. And then she has Sitri Soul, which outclasses everyone in this battle royale when it comes to hand-to-hand combat. She is very powerful when it comes to attack, speed, stamina and magic power.
3). Laxus
Even though I think Laxus will surpass Mirajane in a solo fight, I think he has less luck in a battle royale than Mirajane. In this battle royale, I'd put Laxus slightly under her. But still, Laxus attacks are really powerful and his speed and stamina surpasses the rest of his opponents in this fight. Laxus' attack against Ajeel was really high in AoE and would've defeated Ajeel if he was hit by it. Of course we shouldn't forget about Fairy Law and Red Lightning, because these spells are really strong as well. I don't think he will have time to cast Fairy Law though.
4). Lucy
Since the Celestial Spirit King isn't restricted here, Lucy is pretty overpowered. And yes, I do think she'll summon him, just because there is no other way she could survive this battle. The Celestial Spirit King his spells all have really high AoE. During the Tartaros arc, he overpowered Base Mard Geer. Once the Celestial Spirit King has been summoned, everyone is doomed. The only thing Lucy needs to do is to use her Aquarius Star Dress to create a Water Barrier to protect herself.
As for the remaining ones, I'd rank them as follow.
5). Jura
6). Kagura
7). Juvia
8). Ajeel