I've never been a fan of GoToMyPC, probably because I was used to VNC when I first encountered gotomypc, and by comparison gotomypc seemed pretty clunky.
VNC works very well, has been around for a long time, and is heavily used in geek circles. I don't actually use any sort of desktop sharing myself much, I use technologies far older and more powerful
.
Alternatively, Microsoft's RDP (remote desktop protocol) has an excellent reputation, but it's not suitable for two-person use; the remote screen goes black when you take over the machine.
For VNC or RDP of those you'd have to deal with configuring your network, NAT forwarding, security, and so forth. I asked one of the sharper networking guys I know and he recommended for an easy-to-use solution, LogMeIn.com.
LogMeIn.com used to have a free option, but that went away last year. I saw a lot of people talking about moving to TeamViewer (teamviewer.com).
Steve