Jhat, I guess it depends on what you want to use it for. I originally built a Guillemot, which is from the same family as the Petrel, and decided to build the Greenland deck Night Heron. I've been paddling that for about 1 1/2 years now and am quite happy. I think both the Petrel and Guillemot are described as 'rough water play boats". On our stretch of Lake Ontario we can go quite a while without any good play waves. With no waves to play in that leaves speed or rolling for fun and the Guillemot didn't shine at either of those activities. Opting for the Night Heron gave me a faster, straight tracking boat for those calm days which still performs well in the rough water. If you live on the west side of Lake Michigan, maybe finding rough water won't be a problem for you and you'll want the Petrel. You probably found this, but the "compare designs" function on Nick's sites sums up the differences nicely.
Mark