Brides.com had this suggestion to offer....
Have a frank conversation with each man and find out who this honor means more to—you may even want to enlist the opinion of your mother as well as your siblings. If you give the privilege to your stepfather, let your father have the father-daughter dance or allow him to give the first toast at the reception. If it seems that both men are equally invested in escorting you, you could give each of them an arm and walk down the aisle as a trio. Or, you can stroll down the aisle by yourself and give each of the fathers a different role to play at the ceremony. One could be a greeter for arriving guests; the other can give a special reading.
Visit brides.com for more ideas concerning "split decisions".