You'll need to begin by looking at your father's medical history and how often he uses various healthcare services. Then figure out how much he's spending on healthcare. You have
to assume that his healthcare spending will go up as he gets older and these health problems become more of an issue.
In your father's situation, he should look at the more comprehensive Medigap plans. With high blood pressure and obesity, he's going to want to make sure that preventive healthcare -- annual physicals, for example -- is covered, which means that Medigap Plan J (the only plan with significant preventive healthcare coverage) is probably the best choice for him.
Plan J could also be a smart choice because of your father's weight issues. People who are obese tend to use almost twice as many Medicare services as those who are at a healthy weight.
It's important to remember that Medigap no longer covers any prescription drugs, so if your father takes any prescription medications (or may need to in the future), he'll need to consider signing up for Medicare Part D prescription drug coverage if he can't get drug coverage through his employer or union.