Well, it would seem that Erza, Kagura > Minerva, as expected.
It's honestly hard for me to get hyped about Minerva at all, especially when Rufus makes a comment like, "She's even more powerful than the twin dragons!" Well I sure hope she is, or that would just be sad.
Kagura is a wildcard, she can be at any level really, but I honestly don't think Minerva is even half the level of Erza, at the most. So I was a little unnerved when she was holding her own against the two, but then she takes a hostage, so that's more realistic. And THEN there's the fact that Erza hasn't even re-quipped once, and Kagura hasn't drawn her sword. So neither Erza OR Kagura have even used magic yet, as far as I can tell.
Hopefully Minerva will be taken out quick, and the REAL fight can begin. I could easily see Kagura and Erza destroying the tournament if they went all out.
EDIT: Also, question. What is Kagura's magic? Has it been shown yet? I'm guessing it's something to do with her sword.