difference between spider I,II,III?

[straymond]

are there major differences between these line 6-amps?

I'm thinking about getting one of these...

[Hikey Mikey]

Basically the II and II are upgrades from the original one. Upgrades in terms of more, not better. I think the basic tone is about the same but later Spiders have more digital tools and effects to shape the sound.