Women with six-pack abs "overegg the pudding," as the British say. They way overdo it. They almost always lose the hourglass figure that makes women so sexy. Their torsos are almost like men's. No thanks.
To me a nice, flat, toned belly, without bulging six-pack muscles, is ideal. It's sexy as hell and maintains the girl's feminine hourglass. It means she's obviously extremely fit (and probably capable of lifting guys!) - but all woman.
I think these two fitness models get it just about right - toned but feminine:
