Sales statistics for the USA are shown on the charts on this page. From the chart above, Prius models are by far the biggest seller with some 236,659 units sold. This represents about 54% of the HEV market in the US.
Ford did well in 2012. The C-Max energi did suprisingly well with 12,000 units sold in just a few months.
The PHEV is the fastest growing EV segment as you can see from the chart to the left. Sales were closing in on 39,000 units before the end of 2012.