Mars atmosphere is thin, almost a vacuum being about 1% of earth. Something those who are big on Mars colonies get upset if you remind them. So it may not make much difference.

A telescope on the moon would be easier than putting on Mars but i guess if you were going to do it on Mars than Olympic Mons would be a good place. We put them on volcanoes on Earth frequently so there is lots of precedence.

The moon has a lower rotation speed so probably has other benefits too.