its actually a little of both..
dont get me wrong, the axiom makes good subs.. there is no problem with them.. but, it is widely considered that the SVS and HSU subs are just a little better.. plus, for the price, you can actually get a more powerful, better sounding sub with the SVS and HSU brands.
one main drawbacks with the SVS or HSU's, is that you dont have as many custom finishes choices.. thats whats really cool with the axioms.. you can get the sub in the same finish as the rest of your speakers.
but i just dont want you thinkin that the axiom subs are bad.. if you had to put it on a scale from 1-10..
$5000 dollar velodyne is a 10..
$600 dollar SVS or HSU is a 9..
$500 dollar axiom is an 8..
my $215 dollar cerwin vega is about a 6..
the little sub in the sony 'HT box set' is about a 2..
a cardboard box with a hamster in it is a 1.. maybe..
hope that clears it up a little..