I know I'm late to this party because so many people have already responded, but I really don't understand how a "second opinion" applies to your case.
You actually have four doctors telling you to have surgery soon, so I think that decision is covered.
When it comes to the type of valve, you actually have no opinions, because the surgeon left it up to you. At first it sounded like you had already decided on a mechanical valve, but now it sounds like you aren't sure.
When it comes to valve type, I think asking people -- like the people here, for example -- who have the various types of valves how they are working out. Think about the way you like to live your life and if the type of valve will fit into it. I don't think an MD can help you make that decision, although come to think of it, a counselor or psychologist might, because he or she could help you weigh the impact on your life of coumadin vs. more surgeries in the future.