Having owned/tested a bazillion button compasses I have a definite preference for the Suunto Clipper.
It has proven to be more accurate, easier to read, and less prone to magnetic interference than all others.
Almost every other button compass I've used will be easily thrown off by close proximity to a metal object, and that is my basic standard for reliability.
I put the compass on my diningroom table with no other metal objects nearby and align it to read North. I then take a SAK and gradually move it in closer and closer until I'm directly above the compass, if the needle moves *at all* it can be considered useless.
Silva and Brunton compasses have failed this simple test almost every time, thus I have absolutely no confidence in either brand.
The only other button compass worth looking at is the PYSER NATO from Tadgear, very expensive but tiny and utterly reliable.