Advantage plans are generally cheaper with little or no premiums and often include dental, vision, etc.
And some Advantage Plans also include Part D.
Supplemental plans (mine has no deductible) has no pre-certs, I see whatever specialist/doctor I want (so I can keep all my doctors I had before).
But surprise, surprise, not always that cut and dry. Some states offer supplemental Medigap Policies called Medicare SELECT which call for In Network care. There is no end to it.