Electrostat - M-L; Quad or Soundlab - reliable

What is your definition of reliable? Electrostatic speakers will require the panels to be replaced, much like tubes, but longer lasting. My opinion is (take ML for example) that the panels are very good for 5 years and typically get replaced in the 7-10 year neighborhood. It is my impression, like with tubes, that people don't notice so much the reduction in performance as the panels start to weaken and that is why they typically stay on a bit longer than they should. This being said, the panels aren't really that expensive.

I will not tell you what is the best of the speakers in terms of performance as you seem to have a pretty good handle on this. As for the Quads, I sense there are only certain models that really hold resale value and seem to move fairly quickly.

Acoustat. The most reliable E-stat ever. My 2+2's are old enough to vote. Been shipped from Florida to Canada and back by truck freight. With new caps and wire (under $100) they will outperform the Quads (just like they always did, read the reviews) and almost match the expensive and unreliable Soundlabs.
Maggies are totally different animals, though they look like e-stats they are not.

For most users, Quad panels last 15-20 years before requiring refurbishing. I do not consider that to be unreliable.

According to Roger Sander's the Innersound panels have never failed.