My tests so far w/ MSE is good for basic users, noobs, techno-phobes - auto updates, seems to be low on resource usage, lets you allow/disallow files, and has a nice detection rate. It does it's thing in the background and leaves you alone. The scan function seems like it's a bit quicker now, but realistically I dont hold scan rate all that high on the priority list. It shouldnt get to that point. Nobody's perfect, stuff slips thru as attacks become more sophisticated, and you should have a firewall enabled to help, but still if youre catching things in a scan at a later time it's not doing it's job sufficiently at present imo.
As for the advanced users, people that can put up w/ some nagging n stuff I'm a steadfast Avira advocate, I think it's an excellent free product.