Single speed, geared, Front mech, no front mech, Intended use ie, pump track, bmx track, dirt jumps, play biking, steps, drops etc, bit of street, local xc bits and bobs with some urban riding too.
Have a think about the places you are likely to use it and take from there. Something with some ability to move the saddle up for road bits can be a good idea,( ie lengthening the cockpit) as such bikes can be nice and small with the saddle down.
Although others probably know more.