Atmospheric conditioners or ringworlds?

[PvK]

I've often (almost always) acquired a complete set of all the atmostphere-type-breathing populations before I get atmosphere converters, so they become unnecessary, unless you're in a game where some breather types are unavailable or non-existant, which is the case in a couple of my games where I haven't got far enough to research atmos converters anyway.

PvK