I had a Rocktron Multivalve (basically an Xpression with channel switching and a tube) I did like it a lot. It sounded really nice and is easy to use, great unit. No complaints. I chose the Multivalve over the Xpression because of the channel switching option.
However, I decided to take a chance and upgrade to the G-major 2, I wanted something a little more current and was hoping that the effects would be better since my multivalve was at least 10 years old.
I have to say I am very pleased with my G-major 2, it sounds great and seams built very well. I do think the effects sound better/have a little more clarity.
Regarding the line 6 stuff and I do like their products (I have owned a Flex tone II, XTL, Pod XT, Pod Pro XT, DL4) I think its good stuff for the price but the effects do not have the clarity of either the Rocktron, Lexicon or TC stuff. I did hear the M13 that my friend bought and I was impressed with what I heard, it did seem like an improvement over the XTL effects.
I am happy with my choice of the G-major 2, it gives me all the options I need and works great for my needs. The channel switching is nice to have even though I am not using it since I bought a Voodoo Labs GCX switcher.