Medicare Advantage (Part C) plans cover Part A, Part B, and usually include Part D Prescription Drugs. They are a true alternative to Original Medicare.
By comparison, Medigap supplements Original Medicare coverage and doesn't cover Part D (you'll need a separate plan).
Typically bundled in Medicare Advantage, not included under Medigap.
Some Medicare Advantage plans may have network restrictions; Medigap offers more flexibility to see any provider that accepts Medicare.
Medicare Advantage plans often have lower or $0 premiums, caps on out-of-pocket costs, but may include copays, whereas Medigap has higher premiums but fewer out-of-pocket costs.
Referrals are typically necessary within Medicare Advantage HMO-style plans; usually not needed with Medigap.
Medicare Advantage plans usually includes extras like dental, vision, hearing, and wellness benefits, rarely found in Medigap plans.