Any coating that is “clear”, i.e., without pigment, will not provide protection against UV exposure. A finish coating must contain pigment in order to block, absorb or reflect damaging UV rays. Stain pigment protects your deck's surface much like sunblock lotion protects your skin: both prevent the top surface layer from drying out and aging prematurely.
When dry, oil-base products will provide a deeper, shinier finish on the deck surface, while water-base products produce a flat, or matte appearance. Be sure to follow the product label's directions on recommended number of coats, so that you achieve the product's intended finish look.