Shana, no matter what you choose, it will be a good choice. Bare in mind that things may get changed at the last moment when your on the table. Sometimes what you want or the surgeon wants to use, just won't be biologically compatible and therefor, you should have a backup plan in mind. Be sure to discuss this with the surgeon when you see him.
My personal fit for you would be mechanical. You really don't want to have surgery again and again. The coumadin is not a big issue at all. It just sounds complicated and hard to deal with, when in reality, it's like taking any other pill or vitamin. Even with a mechanical valve there is no guarantee that you won't have to have another surgery but the chances are much lower then tissue which virtually guarantees that you will.
It's a personal choice that only you and your surgeon can make. Like I said, no matter what you choose, it will be a good choice.