As a rule of thumb, I would probably choose an experienced therapist in private practice, rather than go to an online agency with fresh-out-of-grad-school therapists.

Websites keep up to 50% of the fees you pay for online therapy. If their services are cheap to begin with, and the therapists only get to keep part of that fee, they really don't earn very much. Why would a skilled therapist agree to that when they could earn much more in private practice?