Detection rates are one thing, and of course very important. But those great detection rates may end up being of little use in the real-world if a program lacks certain useful needed important features that allow it to live up to its great detection rates.
At least with me, I want features and features, and options and options. Only with them can an anti-malware program be "custom made" or tailor-made to each user's own personal use and habits. It is this "custom tailoring" which can actually give perhaps a slightly lower rated program the edge in actual use.
There's also popular well-rated AV software that can be had for free after rebate. While totally free AV software usually isn't very good (you generally get what you pay for), paying a decent amount for it then getting it back in a rebate seems the best deal....as long as it is highly rated.