A friend of mine had GT-8, just a year ago. I told him not to buy it because Boss is not very good with multi-effects, but he didn’t listen. And guess what? Just 2 weeks later he was selling it because distortion on it sucked totally.
If you’re planning to use distortion models from it – than avoid GT-8. All you’ll get is a loud ZZZZZZZZZZZZ.
Another friend of mine has a PodXTLive and it rocks. Distortion models sound amazing and you can always download new patches from Line6 site. If i was to decide – i would go for Line6.