There's much controversy over the power level of these two ABs. There're strong hints that they're close to abyssal level but they were never confirmed to be at the level of the original three that ruled the land until Priscilla came along. What do you think would happen in an all-out fight between them?
What we know:
Europa is at abyssal level (contrary to what Malak is saying). There are several hints that suggest that:
a) She was considered as the strongest of all ABs that gathered near Rabona
b) She seemed to know exactly what makes an Abyssal an Abyssal
c) She wasn't overwhelmed by Miata who is at least as strong as Riful/Isley
But hints aren't enough to say that. The thing is, Yagi has flat out said it. Not only characters call her an Abyssal (Galatea, Audrey and others, and Galatea knows what she's talking about) but also a narrator (i.e. Yagi himself). Anyone can check chapter 141 or previous ones and at the end or the beginning Europa is being referred to as "Abyssal".
What we do not know:
1) How strong is Rosemary. After all, we've only seen her in a fight against the strongest Claymore that ever lived and we do not have a reliable benchmark. For that Yagi would have to show us the fight with Hysteria at least or reveal her power in some other way.
2) How strong is Teresa so that we could have a better idea of how strong Rosemary was. We know that 10% she was stronger than 70+% Priscilla but for all we know Priscilla at 10% could already crush Rosemary (or Isley or Riful).
All in all it comes down to preference. Personally I think that Rosemary was at least as strong as Riful/Isley and against Europa (who should be roughly of Riful's/Isley's calibre) she would better chances than Europa against her (so at least 60-40 for Rosemary-Europa).
It what we need a extra special chapter histeria vs Teresa, vs Rosemary in the same special chapter /
We know for what they said an Teresa special chapter, that nobody realize that the one who really kicked histeria ass was Teresa since nobody realize that it means she probably beat her at the same level wen she face it the execution team which was it her basic level or normal level /
now we know how histeria give it at hard time at one of the most fastest claymore known miria /while miria almost awakened histeria was a her basic level -that gives a little idea of ho strong Teresa was again histeria and how strong histeria was again miria.