If its sensible shoes time, I'd go for the Focus TDCi 115hp. Having had plenty of chance to drive them both that and the Fabia RS, I'd chose to Focus as a family car. Still plenty quick enough, more room, more practical and still better handling car. The Fabia is a great little car, good performance and good fun to go boy racer baiting, but it is a little car, only Fiesta sized. The 307 just doesn't impress in the same way, yes its roomy and has a nice ride, but the handling isn't that sharp, and they are very lardy things, and don't go anything like as fast as you think they should with a 110HDi engine.
Just be sure to get a very good deal on the Focus as the new version goes on sale in two months time.