Well, how are you getting the griffon or warcat? It might make a difference.
Also, flight. Flight is something I always look for in a mount.
But then again I don't really use mounts offensively, I typically build mounted archers.
Aren't there some cavalier archetypes which can help in getting this kind of mount?
I have a Paladin who rides a Griffon and I'm thoroughly enjoying it. Note that in order to fly on the Griffon you'll need not only the Monstrous Mount feat but the Monstrous Mount Mastery feat. Also, if you go the Paladin route, take a look at the spell Saddle Surge. I have a wand of it, use it on the first round of many battles, makes the Griffon's pounce even more brutal. Well worth the 6k it cost.
No opinion about the Warcat.
Personally, I don't think it's worth it to use Monstrous Mount Mastery feat to get a flying mount.
Spending two extra feats to get a flying mount...just not worth it.
I'd find another way.
If you can choose a Roc though, I'd do that.
That's probably true, at least from an optimization point of view, but I have to say that from a fun point of view it's pretty awesome to have a flying mount, especially when combined with Wheeling Charge. Many mounted characters are lucky to get a mounted charge in once/fight, whereas my character frequently does it every round.
The griffon has an advantage of being an intelligent magical beast. So it can communicate with the party.
The griffin understands common but does not speak it (per the bestiary)
The griffin understands common but does not speak it (per the bestiary)
. Give it a point of linguistics and it can pick up sign language and write in common with its talons.