The Mode Selection Buttons do the following:

>> VSR Standard:

This is the regular mode which features all of the core VSR balance and physics changes.

>> VSR Plus:

This mode has everything that VSR Standard has, in addition it also contains Smart Scouts (improved dogfighting AI, weapon linking), undeployable recyclers, and the ISDF and Scion teams gain access to the Hammer and Brawler rocket bombers from the Forgotten Enemies mod.

>> VSR Experimental:

This mode contains everything that VSR Plus has, in addition it also contains some experimental new features. These features consist of the following.
 - Buildable Portals
 - BZ1-Style Satellite View (access satellite view from any location)
 - Improved (DLL driven) recycler undeploy

>> Stock Mode

This is used to reset map defaults to use stock 1.3 (non-VSR) ships and recyclers.