I've used both.

I like helmet or glass-mounted mirrors because I can direct the view area by moving my head. Take-a-Looks are my eyeglass mirror of choice. I don't like the too-small size and I sometimes have to think about focusing my vision on the mirror.

I've recently begun the switch to handlebar mounted mirrors. I like the size and clear view offered by Mirricle mirrors. I don't like how they stick out and are so easy to bump whenever I transport my bike. I'm having difficulty finding the right hardware to mount a mirror on my Kettweisel delta trike.

Bottom line, I find eyeglass mirrors are easier to direct what I see but handlebar mirrors let me see it much more clearly. Either will likely need adjusting at the start of every ride.