The main problem with any transplant is that unless the donor is your identical twin, you will need to take anti-rejection drugs for the rest of your life. These anti-rejection drugs will suppress your immune system, making you more vulnerable to bacterial and viral infections.
Today's best option for a functional sensate penis is a metoidioplasty after hormone therapy grows the clitoris to a small penis. It may be a bit small, but at least it is your own penis.