Most of my experience is in 500 series Citations (Citation I, II, V Ultra), and I find that cockpit very comfortable for the most part. Much better than the Lear 25/35. I wish they had more legroom or that I could at least put my legs up between the rudder pedals like I could in the King Airs, but that's a minor gripe.

As far as climate, 500 series Citations are HOT in the summer on the ground. It's got a major greenhouse thing happening with those huge windows. It's a plus in the winter on a sunny day, because it stays nice and warm during the day, but at night it can get very cold because, again, those huge windows radiate a lot of cold into the cockpit. Most of the Citations I've flown are equipped with optional Freon A/C, so at least you can make an attempt at keeping cool on the ground in the summer - not the greatest, but better than nothing. In cruise, you can pretty much always find a comfortable temperature during the day, but again, at night they can be on the chilly side. I try to remember to bring a sweater if I'm going to be flying at night, even in the summer.

The visibility in Citations is excellent. Better than most piston singles. The other jets I've flown, Lear 25/35 and Citation III, the visibility isn't quite as good, but acceptable. Just something you get used to.

I'm sure the Gulfstreams, Challengers, and big Falcons offer even more comfort, but they are much longer range airplanes than what I fly, and need to offer more comfort for a long haul.