Logmein and Teamviewer are both excellent choices. Logmein has ignition to have a "master control pc" that easily connects to all PC's. Teamviewer does the same.
Since you are a "commercial" application, Teamviewer will be more expensive. You can use Logmein "free" for the PC's you are logging into, and pay for the ignition (great setup). The pay version of logmein for the remote PC's don't give you a lot extra unless you need to perform IT type maintenance on them....
It looks like you need logmein pro for file transfer?