Originally Posted by
Kommisar89
Define "better off" - there are basically two things: if all other things are equal, a mixte frame will be slightly less stiff than a diamond frame and two, all things are rarely equal as the vast majority of mixte frames are hi-ten steel and the "ladies'" equivalent of the entry level mens' bike. There are a few exceptions to that but not that many. But is your girlfriend a strong enough rider to notice a bit of extra flex in the frame? Does she push the bike that hard? If high performance is an important criterium then go with the diamond frame. But if she's looking for a nice comfortable bike to ride the local MUP than a mixte is fine.
I would echo just about everything here. If your girlfriend is looking for a traditional mixte (parallel top-tubes) the latest is the Buena Vista from Soma (~$500 frameset). Or, try tracking down a solid chromoly mid-80's Japanese mixte. I also hear that Peugeot mixtes from the 80's using "HLE" tubing are decent. Although I've never ridden one.