Juri, this question come up often, you're asking which atmosphere comes up most. That's easy, just take ancient race, and count the planets screen.
A related question, what atmosphere type gives the most facilitys, depends not only on the distribution of atmospheres, but planet size and type as well. There's have a little (slightly screwy) description here
{Wiki} , which actually links back here to an old post by Andres Lescano
