Manuel: I'm not an "upper", but rather a "downer" (i.e. rappelling, canyoneering) so my needs might be slightly different from yours. But if you're spending any time hanging from it you'll want something that is comfortably padded and fully adjustable, which may end up being more bulky than what you were intending. I use a Petzl Corax. It has fully adjustable leg loops (a plus if you are on rope for any length of time) and an easily safety-checked (by your partners) double buckle at the waist.
Not sure if that fits your criteria.
I'm not a bouldering or gym rat so I can't speak to its utility in those applications.
Steve
