In terms of pure strength, as the series is now, ram would win(since rem doesn't even remember how to fight). if we are considering arcs 2 and 3 though, rem would win because of her horn, and if we are talking about the oni village times, ram would win because she is times stronger in general(only loses nowadays because she lost her horn).
In terms of waifu material, i have to give them the tie, ram got her points up during arcs 4 and 6, enough to compare to rem
Naturally, Ram is stronger as she's the second coming of the Oni God. However, she can't normally access that power, making her weaker. So... you actually have two answers. Either Ram>Rem or Rem>Ram. Both are correct and both are false.
Under normal circumstances, Rem is stronger. If Ram has access to her Oni abilities, however, she'll win. If it's Arc 6's climax Ram, then she'll one-shot Rem in a sec.