I was told by my friend who works at a Yamaha store that the Line 6 POD is an amp simulator with effects, just like the Johnson J-Station, but then there are multi-effects units which also happen to include some amp simulations, like the BOSS GT-5, or Digitech RP series.

So it would seem that it depends what you're looking for. If you're wanting to play direct into a P.A. or mixer, you would want an amp simulator. But for people who have a good amp already and just want a lot of effects without spending big dough and pressing 18 pedals at once, a multi-effects unit is the way to go.

Just wanted to share the results of my research from a few weeks back when I was looking at buying a multi-effects unit.