That's a very difficult question to answer!! I have been to both, and am going back to both in a month or so.
Last went to Coron three years ago, and have heard that it is a little more developed now... The locals were just finishing surfacing the road from the airport to Coron town back then. Amazing scenery, a kind of frontier feel to the place, and great wreck diving. Also a thermal lake to dive, and Cathedral Cave. This trip we are heading North West of Coron town for a few days, looking for the Dugong... We may be lucky, but I suspect very luck is more realistic! It will be interesting to see how the place has changed, but am sure will come away as impressed as after my first visit.
Have made three visits to PG.. Different type of resort and different type of diving. Great reef diving, great macro, a wreck or two, and Verde Island too!
There is no answer to your question.. Try and do both.. If you are flying into Manilla it is easily possible to do both in a fortnight.