When it comes to buying new Apps I prefer to purchase directly from the Developer. Necessity requires an occasional purchase form the Mac App Store though. Previously, I have provided reasons to not use the Mac App Store. The recent discovery of security issues with some of the Apps sold there is just another reason to avoid the App Store. Yes, third party Developers Apps can be corrupted also, but they can provide a lot more focus on App Security. I think the bottom line is the App Store has so many Apps Apple is not able to guarantee that each one is secure. There is just too much volume. The above linked article on security issues is informative, check it out and decide.