This question haunts me again and again. I have a POD HD 500X, a Line 6 Spider and a pair of Mackie monitors. The patches sound really different when I record / mix if I create them using the amp. While recording, I plug the output of my pedal into a mixing board which goes to the Audio Interface. My guess is since I am modelling the Amp in POD and not using a mic to record my amp's output, I probably should use studio monitors to get a sense of how the guitar will sound like when mixed into a multitrack song.