It all depends on the saddle, you can get uncomfortable English and western saddles alike, you can also get good ones of both. Its kind of difficult when riding in a saddle that isn't yours, I often find RS saddles uncomfortable on the odd occasion I go to a RS. Getting hot is probably more to do with what you are wearing and the climate rather than the saddle specifically, what you wear can also drastically improve general comfort/rubbing etc
I ride both English and western, I like knee length boots (or short boots and gaiters/half chaps) for English as the stirrup leathers can pinch otherwise, in western I can ride with long or short boots as there isn't the pinching issue.