The GE Mark 1 is the absolute worst. It's the most crowded, humid, and hot containment out there. There's no room to stand, no room to walk, and virtually no way to get aloft without climbing. I did my NLO time in a Mark 1 Containment. Even during outages they rarely get below 110 degrees F in most places.
Next worst is an Ice Condenser Lower Containment I guess, though it's larger than the largest Mark 1 Containment with smaller equipment. It's not as humid, there's more room and the temperatures aren't as bad as a Mark 1. The accumulator roms are close to the feeling of a Mark 1 but not quite as bad.
Mike