The alpha versions are the most recent development versions of the modules which may or may not be stable. If you want the latest and greatest features and bug fixes, go ahead and grab the alpha versions. If you want the most stable versions, stick to the release versions. If you have Curse Client, you can download alpha versions by simply right clicking on the addon in your Curse Client and under "Add-on Type", switch to "Alpha". To manually download alpha versions, find the project on CurseForge and go to the "Files" tab.