My Mom has part F and it is the best. It covers the deductible at the beginning of the year. I have part G which is the next best BUT I have to pay a small deductible at the beginning of the year, less than 200, then no more deductible.
My mom's part F is "grandfathered" in but she will lose it if she changes from part F.
Go to the Medicare site to read about this.