I have had both (plus numerous other Continental breeds) and it really boils down to if you do more upland than waterfowl over water and you want a dog that points, then a Griff would be a better choice. If you mostly hunt waterfowl over water with occasional forays into the uplands and don't mind a flushing dog then a lab would be better. They are both Jack of all trades with a slant to one side or the other from the middle.
As for disposition, the Griff would probably be a little calmer but that is a very general statement subject to the individual dog and how it is handled/trained. A buddy has field trial bred labs and they are very well behaved, better than the vast majority of dogs out there. But, he instill obedience in them from an early age and enforces it. My Griff (and other dogs) were generally not as well behaved but I wasn't nearly as strict either.
My preference would be for a Griff for all around hunting and house dog but I do more upland hunting and do not hunt big water for divers so my retrieving needs are more modest. Other than that, it would be a toss up for me.
