Zipline's work in Rwanda is really inspiring. I love that they are doing real good in the world first and can leverage that to grow their commercial business.
I imagine it depends on the size of delivery. Even with extremely good roads, zipline would probably be faster (I can't imagine that flying in a straight line is _ever_ slower than driving), just lower bandwidth. Single small package? Zipline is probably much faster. Many and/or large packages? Driving is almost certainly faster. Good roads don't change this basic fact, they just change the break even point.