My opinion on the matter is based upon crho post. Crho (contrary to all other people claiming that either of trackers is better) provided links that support his claims (link to crho post).
Famitsu coverage rate - over 80% for console and 60% for the PC market.
http://www.f-ism.net/fmds/index.html
Media Create coverage rate - approximately 57%.
http://www.m-create.com/biz/data.html
Differences between MC and Famitsu are sometimes quite significent and I don't think (as some posters in this thread) that the matter is of no importance.