I'd go with what matches your skin color best. Sometimes i wear a thin pair under my thick pair because my legs stay warmer in warm up.
I like the ones that are not OTB, but my skates are so beat up right now, I would opt for OTB. Some brands are REALLY thin, so go with Mondor. Now they make them with velcro instead of snaps which makes EVERYTHING so much easier. I like to re-lace at the last minute, which may be a bad habit, but the velcro simplifies that stress!