For planet-wide real-time communications (i.e. voice) you really need several server locations or go p2p. Optimize for MOS ( https://en.wikipedia.org/wiki/Mean

For planet-wide real-time communications (i.e. voice) you really need several server locations or go p2p. Optimize for MOS ( https://en.wikipedia.org/wiki/Mean_opinion_score https://en.wikipedia.org/wiki/Mean_opinion_score ) and take into account how latency affects that score.