WD is coded by people who can actually write code that won't screw up your machine. Most of these 3rd party AVs will do more damage than malware. Just take a look at their forums.
Any solution will have their ups and downs, including MS own solutions.
One thing most people do not realize is that any 3rd party solution is coded to work with a set of modules/rules/dlls from the OS itself, so it is only fair to have problems every now and again.
avast and BD forums for example, most issues are not related to the OS, but to the actual software coding and lack of full bug testing prior to release, unlike Kaspersky, Norton and others.
MS has its fair share of release of fixes without proper QA testing.
As for OP, voted WD because it does what it says on the tint. Doesn't have the features that Panda has but for me is perfectly fine.
Panda had its fair share of FPs, however bear in mind that in the past such FPs affected windows system files, rendering systems useless across the world due to a bad update. Not to say Panda is not good, because it is, however I would prefer less bells and whistles if it was to choose between Panda and Windows Defender.
And I have used both, along with other solutions.