Free: MSE is the better one out there. I personaly have a very strong dislike for McAfee. I know I'll get hate response here but I do not recommend end users use Free based AV clients. They are free for a reason. It's called marketing. The paid versions are always better and offer more protection. It is true that tech savvy people can often times get away with a free based AV client. However none technical users need more protection. Spend the money and purchase an AV client.
Paid clients I like. G-data, Spyware Doctor with Antivirus are my top two. Very user friendly and more then adequte protection from just viruses. If you are looking for a spam filler as well I would go with Kaspersky IS or Bit Defender IS.