I've had several good experiences with TeamViewer and plan to switch to it pretty soon once I verify my research. Reasons include (not that some of these aren't in other products):
1. It's free
2. It can be installed as a service on the destination remote PC to allow remote unattended. So far so good with this.
3. Multiple people (TeamViewer clients) can connect up to the same common TeamViewer host session
4. I have misfortune with GotoManage (formerly GTA Express) that others here don't such as:
a) Group sessions significantly slow down once a GTM person joins
b) In group sessions, mouse and keyboard control goes haywire when GTM person joins
b) On secure server environments it cannot join into existing RDP session. It connects me to the console session instead of user's desktop session. I work around by connecting to client's wkstn instead of their session but then I can't transfer files easily.
b) Cannot do unattended remote session to Server 2008 and Windows 7 64-bit PCs when their UAC is turned off (says in the doc it may not be able to send Ctrl-Alt-Del with UAC off)
My only complaint so far is it can only display remote PC at max screen res of 1280 x 720. I would say give it a trial run first.