Trader Workstation Latest: The most recently promoted production version of TWS. Contains all of the latest and greatest features. Hold your mouse over the version to see build number and date.
Trader Workstation: This version has been around the longest and is updated less frequently. It won't contain all of the latest and greatest features.
Trader Workstation Beta: The beta build is still being tested and is subject to change. It's still a live trading platform, but won't be considered "complete" until it becomes the latest production build. This version will have even more features than the latest build.
NEXT STEP: Select the Mosaic Workspace