Both shows take historical male characters and turn them into busty kick ass ladies. Very entertaining and not to be taken seriously at all. Battle Girls are in their own land and get a normal human transported to their world where Sengoku Collection takes these historical figures and transportes them into our time! Check em out.
Both series feature girls in a fantasy world with mostly medieval technology. Both series are not afraid to portrait their female characters in only their undergartments and both series have about the same general quality and depth to their characters. If you managed to like either I'm sure you could manage to like the other somehow.