mybass has pretty much nailed it. If space/portability is major issue, get the traveller cabs, but they are of a lesser quality than the standard series. I can't tell you which speaker size is best to go for, but I used to own a 4x10, sold it in a moment of madness, then got another because of how much I loved it. Whenever people put their head through it at gigs they are full of compliments about the sound and how efficient it is, so I can definitely recommend a 2x10 / 4x10