Darth Vader and Revan lose. Total curb stomp.
Sidious is the most powerful Sith ever, meaning Vader and Revan are both inferior. Yoda is superior to both Revan and Vader as well. Thus Darth Vader and Darth Revan go down hard then Yoda and Palpatine enjoy a victory smoothie.
Sidious could take them both at the same time with ease.