Both prism styles are best for bird watching but when it comes to image clarity, Porro prisms raise the bar high for producing high-contrasting natural images of distant objects.  Porro prism increases triangulation and redirects the light several times to offer you a good spatial vision.  However, it is the size and weight of the Porro prism binoculars that can force you to think otherwise if you are in no mood to carry extras during the trip.  This is where Roof prism binoculars come as a rescue for their compact construction and hence suitable for versatile uses in concerts, games, stargazing besides treating you with amazing nature gazing and bird watching experiences without any strain.  Roof prism binoculars are also expensive as compared to Porro prism because of all the science put behind in making them.