Penetrating finishes are recommended for use on wood decks. These finishes include water-repellant preservatives, colored water-repellant preservatives, and semi-transparent stains. A penetrating finish applied to wood decks provides better overall performance and is easier to apply/reapply than a film-forming finish (e.g., paint, solid-color stain).

Clear, Toners, Semi-Transparent's and solids are your choices. Which one do you want?

Solids: Solids are film forming, meaning they do not penetrate the wood. They are basically a thin version of paint. They provide a dense, opaque, film forming finish. Solids obscure the wood grain, are prone to peeling and cracking over time and will eventually wear off the surface. Solid color stains are available in oil and latex-acrylic based formulations. Acrylics are less likely to peel since they are more elastic but harder to remove should you change your mind on color in the future. Humidity trapped in the wood will eventually push and crack either as it tries to escape. An obvious advantage to using a solid color stain is the amount of colors to choose from. A disadvantage is your finish will crack and peel and could be more costly to restore or stain. Cedar, Cypress and Redwood should have a primer put on first to prevent the tannins (blackish/brown extractives) from migrating to the surface thus discoloring it.

Toners/Clears: Toners contain trace amounts of pigment and are still considered transparent. They come in various hues and allow the wood grain to show through while providing some color. The pigments do block some of the UV rays and many contain mildew and fungicides. Clear coatings are for those that want to retain the natural color, texture and pattern of the wood as much as possible. Penetrating coatings, not polyurethane's or marine varnish is what is used. The most protection you can expect is water repellency and mildew/fungicide.

Semi-Transparents: Semi-transparent stains contain enough pigment to make them partially opaque and more resistant to damage from the sun. Visually they reveal less of the woods grain and texture. They penetrate the wood by soaking into it which prevents peeling or cracking. They will fade over time but are much easier to strip or reapply. Ready Seal has one of the highest amounts of  pigment/solids in it offering optimum protection.