I don't know about Mint, but gOS, is IMHO vastly inferior to Ubuntu. Try the Ubuntu Live CD. The Knoppix Live CD is kinda useless for "trying out" a distro since it's non-trivial to get Knoppix as a permanent Linux distribution. It's kinda beside the point anyways, as Knoppix is specificalyl designed to be a Live CD. However, the Ubuntu Live CD will give you a good idea how the actual Ubunut will feel like (and the Live CD IS the install CD - so if you like it, you just double click on the installer). Just expect the installed versions to be orders of magnitude faster than the Live CD, especially when it comes to program start up times.

Martin