Either these garbs- Pyjamas or T-shirt with shorts.
I like wearing the t-shirt garb the most because it is really comfortable. I would actually consider that as the second most suitable garb to wear. As for pyjamas, it's also comfy bu sometimes it irks me out since its too transparent and it is long sleeved. If it is long sleeved, I won't get any air.
It really depends on the temperature indoors and whether or not I'm comfortable. Exercising in the late of night has been a hard-to-break habit, so in times like those I don't really wear anything but boxers and a tank top. Actually, no matter what the case, it's usually a tank top with or without sweatpants.
It kind of depends. If I'm exhausted, I'll simply jump into bed in whatever I happen to be wearing that the moment. When I do bother to change my clothes, I get into pajama bottoms and wear the same shirt I wore that day. I don't wear socks to bed unless it's cold.