Bestform in Keybindings doesn't seem to have any function at all. Nothing happens in any form

CastShapeshift form is PROTECTED https://wow.gamepedia.com/API_CastShapeshiftForm

This cannot be implemented in an addon.

Suggest using the follow macro:

/cancelform [stance:1] [stance:3]
/cast [swimming] Aquatic Form;
/cast Travel Form