[Wavytone]

The challenge is to define “best”. It’s a trade-off between many variables and everyone will rank them differently in importance.

Significant decisions by professionals usually use MultiFunction Attribute Utility Theory or Analytical Hierarchy Process to weight the criteria and score the alternatives, not seat-of-the-pants “I think” type answers. Weighting is usually done with pairwise comparisons and Gaussian elimination.

For the SSO site selection the criteria included political stability of the country, availability of engineering, construction, accommodation, transport and other services needed. Of the optical criteria the percentage of useable observing nights (ie cloud free) was the most important, seeing was a distant second.

FWIW the altitude of Mauna Kea and the ESO in Chile put them above the worst of the cloud.

There are locations in western China (Yunnan), Tibet and Nepal that likewise are technically tropical but their extreme altitude means they are probably quite good locations if you don’t mind the political and social aspects entailed.