The free version allows you to manage up to 5 PCs. It has ActiveX, Java, Firefox extensions and even an HTML based client. LogMeIn is great for accessing Windows PC over the internet and also supports ActiveDirectory integration.

Remote Desktop works well over LANs and integrates seamlessly with ActiveDirectory.(Think dialup connection) And it works on virtually any platform. VNC actually performs better than the other protocols over extremely limited bitrates.

I've used VNC, Remote Desktop, LogMeIn Free, PCAnywhere and remote X. Remote access services do have the benefit of being able to punch through firewalls easier than direct remote access, they are usually easier to configure and have better support for encryption. Other proprietary remote access services may use similar techniques but are undocumented. This is why under some conditions they are superior to VNC. RDP and X protocols transmit drawing instructions instead of patches of pixels. Any client can connect to any server because they negotiate to determine which protocol features both support but its best to use a client and server from the same company if you want to use more advanced protocol features. You can fiddle with the settings on both the client and server to see which settings work best for your internet connection.

Various forms of lossless and lossy compression.

Copying cached regions on the client when changes do occur.

Only send changed regions, caching unchanged regions on the client.

There are a few optimizations VNC servers/clients already do: The higher the resolution and bit depth the more bandwidth required to send updates. RFB, remote framebuffer, works by transmitting rectangles of pixels over a network. VNC has some limitations inherent in the protocol it uses.

Nx vs vnc