You should consider the late enrollment penalties CMS will levy if you do not sign up for Part D when you are first eligible.

Some companies offer lower premiums and deductibles, though they compensate with higher costs (or lower benefits) elsewhere. If your current drug costs are low when you first become eligible for Part D, you may still want to enroll in a lower cost plan when you are first eligible, in order to avoid late enrollment penalties when you are older and may need more comprehensive coverage.