I've had my GSO 10" dob for about a year now and I love it.
Re portability, it fits across the back seats of my station wagon (just). The base goes in the boot. This is definitely worth checking as you will be wanting to take a scope like this somewhere dark once in a while to get the most out of it.
Collimation is important. The scope is f/4.9, so you have very little margin for error with the alignment. I use a cheshire eyepiece for collimation.
There's a lot of reading about collimation available, read what you can bare to. My favourite links for collimation are:
http://www.skyandtelescope.com/howto/diy/3306876.html
http://www.astro-baby.com/collimatio...on%20guide.htm
If you can get the help of someone experienced to get you started with collimation I'd recommend it. I've had to muddle through on my own for the past year, and have had plenty of wtf moments along the way. It's an essential skill to have though.
I have not owned or used a Skywatcher so can't really make a comparison. Someone at a recent star party who owned a Skywatcher 10" was saying that the base on the GSO is a lot smoother than his Skywatcher, and that the GSO focuser seemed nicer.
It's very hard to get any qualitative comparisons of the optical quality of the 2 brands. Everyone seems to have an opinion on this, I take them all with a pinch of salt.
One decision I had to make was whether to get a red dot finder or a finder scope. I went for a red dot but eventually changed to a GSO right angle finder as the lack of any magnification on the red dot finder just wasn't working for me. Some people swear by their red dot finder though.
Anyway, good luck whatever you decide
Malc