I have personally never had the desire to adjust the stem when out riding, but if I did, I would get one that required tools to adjust, and take the time to get a solid adjustment.

I don't know how they would deal with constant changes, but I rode a few thousand miles with the stock adjustable stem on my 2013 Giant Sedona DX and it never slipped.

I would personally get a rigid stem that would get your handlebar at the right position (possibly half way between your two adjustment points, and keep it there and/or adjust height by loosening and tightening the quill bolt.