Both. The two work in totally different ways, one by dampening vibrations and to a lesser extent serving as a "barrier" to the noise (Dynamat) and one by absorbing noise (Paxmate). There's no reason you can't apply Dynamat and then apply a layer of Paxmate on top of it.
Of course if you want the best solution possible, I've heard this stuff is the best noise dampening material available:
AcoustiPack