Hi Cindy, valve choice is extremely individual - what works for me or someone else may not be the best choice for your son. What we can do is relate our personal experience. You're also at that "chicken or the egg" spot, in that lifestyle may factor into valve choice and vice versa.
For a 2nd surgery, and particularly at such a young age, I suspect you'll hear that mechanical is the way to go. This may be true, but please understand you'll hear both extremes of the argument. Mechanicals offer extreme durability of the valve itself, but there are other issues to factor in, like how disciplined your son will be in taking Coumadin / warfarin EVERY DAY; and lifelong exposure to the inconveniences and increased bleeding risk. The bleeding risk is where I see some tradeoffs for your son - if he's injured severely it may be problematic.
There actually have been some (very few) incidents with Coumadin among members here, but I'll let them come forward if they wish to relate their own experiences.
That said, I have 2 mechanicals, but my medical situation dictated that course. Due to radiation exposure, heavy scarring meant that my first surgery was as challenging for the surgeon as most people's 2nd or 3rd. They are more challenging technically each time. Coumadin hasn't been too bad for me to manage - I'm old enough that I've outgrown most of my risky activities. My diuretics have caused me way more pain, frustration, and physical side effects than Coumadin.
But that's me.
There is a really good thread laying around about valve choice started by Peter Easton.
Best of luck to you and your son