The advantage plans will combine their Part A and Part B and D. But you may give up some control as they are managed plans.
You have to look what providers and hospitals are in your area and how you use healthcare, if you like your current doctors and what they take.
You should be able to switch back but the different plans may have their own networks so you might have to switch doctors, etc. if you have only have Medicare, the secondary insurance picks up the copays. The advantage plans may have different copays and out of pocket costs totals.
Also remember that Medicare doesn’t cover international so if you’re traveling, you may need to get health insurance for trips.
It really depends on your needs.