sorry, don't know anything about Yogi or Advanced System care

But if it's any help the latest edition of the uk pc magazine PC Pro reviews a number of anti-virus products, including MS Security Essentials, AVG and (I think, magazine not to hand) Avast. The conclusion was that of the free offerings AVG is the most complete but the the persistent nagging to buy one of their paid for products is somewhat annoying.

However I'm currently using MS security essentials purely because I got sick of the nagging from AVG!