My opinion is both have their place/ function within my reef tank
I have been running both Carbon and Purigen for around 3 years now
I have not found a problem with the regenerating and can renew mine for 4 or 5 times
before deciding to change to new one
If I was forced to choose one, I would go with the Purigen for the simple reason that with carbon its a "feel" call on when to remove and replace , I have never been 100% sure that my chosen schedule of replacing is either, dispossing of carbon with potential to continue removing nasties, or if I am running it beyond its capacity to remove
it removes substances that we generally cannot measure for, and as such indicators from inhabitants or a definite yellowy tint when aquarium is viewed side on, are the general indicators I use
with Purigen the definite colour changing you see on the beads, in addition to the clarity of tank and general indicators of the inhabitants, is a nice bonus IMO, I never have to question myself when it comes to regenerating or renewing Purigen, but with carbon I often find myself doing just that
Steve