I chose to auto-pay via a "push" from my bank rather than a "pull" from CMS (Medicare). I felt I had more control over the payments that way, and it was quicker and easier to set up through my bank (a couple of minutes online) than through CMS. I cancelled my payments after last month's went through, and will get my first Social Security deposit, less Medicare payments, later this month. I've already received the letter spelling out both my SS amount and the Medicare adjustments.
Also note, if you are subject to IRMAA, you will have a surcharge both for Part B and Part D, if you choose to get it.
"I can't complain, but sometimes I still do." - Joe Walsh, Life's Been Good