Yes, there is a difference between the two anti-virus, but I'm not really sure, but I recommend you to use anti-virus personal because in my opinion it's better than free anti-virus.
NO, Avira Free & Avira Personal are different in their vesions, pro manes, & their definitions, along with some features.
Free provides a full time protection but not to all sites.
Personal provides blocking of sites, as well.
Avira AntiVir Personal and Avira Free Antivirus are pretty much the same product. Avira AntiVir Personal became Avira Free Antivirus - it just changed its name. Therefore, Avira Free Antivirus is newer, and probably the better one.