which one has a better sound for PC?

also why is the guitarport close to 2kg and the g2.1 just over 1kg? thought the guitarport would be the more portable of the two.
I've got the G2.1U and have screwed aroudn with the Line 6. they're both pretty good for what they do but if you're ONLY using it for recording the Guitarport owns the G2.1U because of the software and teh ammount of effects. If you want an expression pedal, want to have the flexibility of running it through an amp later on or as a backup in case your fancy tube amp fails at a gig and u need to plug something into the Pa system then the G2.1U is pretty good.

Guitar port = more settings, but dependant on the PC for the effects

G2.1U = all in one multifx unit, has it's own computer in it that processes the effects, the effects are bloody tweakable and should be given a lot of credit, it's 24bit 96khz. It's heavy duty but is still plastic (it's more of a PVC kind of plasic though).

If you hate zoom at least try the G2.1U out, it's like if the Spider III came out and u decided to use all your opinions on the Spider II to define the Spider III, what if that spider III was as good as a pod xt at modelling and was still pretty cheap? So zoom haters, i don't think you're opinions are necessarily valid if you want to share them on this topic.
The Zoom is going to be more portable. It is an effects pedal pretty much. The Guitarport is simply the middle man between your guitar and computer. They are actually 2 different things that can't really be compared well.

The Zoom is better for gigging and practicing but the guitarport is probably better for recording.
would tone port be the best choice then, that way i get the line 6 software as well?
yep tone port for recording definately. that software looks pretty awesome. I think the Zoom G2.1U does a recording with it's asio drives at a better bitrate but that doesn't really matter in the end because it's so processed.