Both, what I tend to do is use the pod stuff for my amp models and delay as it's more flexible, but use the Garageband plugins for modulation or compression. The GB plugins aren't bad, but they work alright I guess.
There are vastly more powerful pieces of kit out there, but I like it cos it's super simple to use and the sound isn't that bad. Though saying that I don't really mix or EQ anything i record, just set the levels and roll with it.