MSE has always served me well since it's release. It does a great job of scanning, updates daily (sometimes twice), and I highly recommend it to all.
But as I've always stated, having MBAM is a good second scanner to use in addition to MSE. Also, I've recently discovered ESET online scanner, it does well, too.
I've never paid for an AV during my computing lifetime, and never will. There are too many free options to need to pay to keep your computer secure. The first option is the one between the chair and the keyboard, no AV/Malware program takes the place of safe computing.
Cat