The skies have a new holy battler, the Crusader Griffin! I'm a huge fan of the [mwcard=MW1C19]Gray Angel[/mwcard], and I use them a lot, so I wanted to compare them. I know many players consider the [mwcard=MWSTX1CKC06]Guardian Angel[/mwcard] to replace the gray angel, but I think that's giberish since they have completely different purposes.
Manacost
The angel costs 12 while the griffin costs 13 mana. The Angel has thus a very small edge here.
Movement:
Flying vs Fast + Flying, here the griffin has a big advantage. It will most like be able to hit it's target more often and easier.
Constitution:
They both have 2 armor, the angel has 10 life while the griffin has 9 life. There is thus a very small edge for the angel here.
Attack:
4 dice vs 3 dice + charge 2. In combination with fast, the griffin can very often strike with 5 dice.
Looking at this I think most people would conclude, and not be wrong, that the griffin is much better since it can hit harder and fast. It is not unreasonable to think that the griffin will hit with 5 dice every attack.
HOWEVER
The griffin is a lot easier to take down! EDIT: It is much easier to stop the griffin from being dangerous! And this is my main concern with him. He is great to take down opposing ground troops, but he's pretty weak once your enemy has its own team of flyers. He will be hindered and will not be able to sprint out of the zone and back again to gain the charge bonus, reducing the attack value to 3 dice. Cards like tanglevine, maim wings, Chains of Agony, ... can all mitigate the strength of the griffin easily and I believe this is the biggest downside of this magestic beast.
Last but not least
The Angel can kill himself to heal something else (your mage of course) 6 dice of damage. If you know that your angel is probably going to die, or your opponent made sure he is useless like a combo of curses, it is great to be able to have some last awesome use out of him. I have heard many people say that they never use that ability, but I have used it tons of times. It is simply a GREAT ability. You don't have to use your mages quickcast in the heat of the battle and it does not cost any additional mana.
I'm not saying the angel is better in every situation though. My priestess will probably change all her gray angels in griffins since she is amazing at supporting creatures. My priest however will stick with gray (holy avenging) angels for now.
Sidenote: In the PVS review, coshade mentioned that it was great to cast lion savagery on the griffin. I agree that you gain a lot of extra power with it, but it makes his biggest weakness even worse.