Bias always for anything curvy because it's the only way to have it lay flat. Sometimes I like bias cut binding because of the design it makes (e.g., with stripes on diagonal). For just about anything else I cut on straight of grain.
And for my tree skirt, I used a silver fringe & sewed it to wrong side & flipped it. You could do that with a nice piped binding or just not bind it at all and save yourself the time & fabric.
