I just body the Withings Body and I love it.
I was considering buying the Withings Body Cardio, but virtually every review said it wasn't worth the extra cost. It's $30-$50 more and the only difference is that it measures your heart rate and it offers a feature called Pulse Wave Velocity - both of which are apparently very finicky and inaccurate. Also, the Body Cardio charges via Micro USB (every 12 months), where the regular Withings Body comes with 4 AAA that last for 18 months.
You can't go wrong with either scale, but the Body is a better bang for your buck than the Body Cardio is.