Is synthetic underlayment better than roofing felt paper?

Without a doubt, synthetic underlayment is far superior to roofing felt paper.  Roofing felt will begin to breakdown and get brittle over the years.  In high winds, shingles can be blown off the roof in patches, and often the roofing felt paper goes with it, leaving the exposed decking vulnerable to roof leaks.  However, synthetic will not become brittle enough to tear off with the shingles better protecting your home from roof leaks.