Would you rather sleep in a Romper or a one piece footie pajamas? I like footie pajamas and as a guy I find it cute when girls wear them! Especially if they were an AB!
I find footed sleepers way too hot to sleep in except for when camping. If I do fall asleep in one I end up taking it off later in the night. A onesie keeps the diaper in place nicely.
Footed pajamas if the weather was cool enough for them. The term romper, to me, refers to a one-piece garment with legs, not a onesie. I don't see myself as a big fan of onesies, so for simple babyish sleepwear, I would choose a diaper and t-shirt over a onesie.
Like FauxPas said, depends on the temperature and time of year. Footies in cold weather, and either a onsie or romper in warm weather. And, of course, always diapered!
Pyjamas! In summer I'll wear long thin lounge pants and a t-shirt, in the winter it's onesies, I recently bought my 3rd. I have a Santa Claus one, crocodile and my newest Cookie Monster