Canon DPP produces very good conversions IMO, and since it's free with all Canon dSLRs I'd start there in the first instance.
DPP has gained some useful lens aberration correction options in the more recent versions; assuming you're using Canon lenses. So, make sure you download
the latest version to get those (choose your OS from the dropdown first).
The only area where DPP falls down IMO is when attempting to recover coloured highlights on overexposed images, where grey tends to prevail.
Silkypix does a far better job on that sort of thing, even if the UI is slightly strange. ACR is somewhere between the two in highlight performance terms. Of course ACR only comes with Photoshop, which makes it far from free. Silkypix is cheaper, but still even that's 150USD.
Don't forget that there are also free trial versions of the Adobe options too though;
Lightroom is particularly popular at the moment.
At the end of the day everyone has their own preferences of RAW conversion software though; I suggest you try anything that seems interesting, and hopefully you'll find something you like!