RealVNC
RealVNC gets my vote. It's a bit more work than gotomyPC as you need to open up the port on your firewall to allow access and remember what IP address your target PC sits on.
As gotomyPC initiates a connection to the internet when it starts you generally do not need to tinker with the firewall and it keeps track of the IP adress for you. However they charge for the service.
To manage your IP address tracking for free there are various services that you can run on your PC that automatically update a DNS server with the current IP address allocated by your internet service provider.
regards
Memetic.