Both are fine for our pond uses.
I've used both, based mostly on price and availability. My local HD has both PVC and ABS in 3" and 4" sizes, but some fittings were twice the price depending on the material, and as was mentioned above, sometimes I could only find a certain bend in one or the other, so I made due with what I could get. Wherever possible I try not to mix them because I don't get a good feel from the green pvc-abs glue but as was said before, we don't have pressurized systems so it's less of a concern. Just be sure to use the right kind of good, fresh glue to join everything together.
-Steve in Phx.
Novice Extraordinaire