Clear sealer
Protects against moisture but gives you almost nothing against UV. On a shaded fence or a covered porch it can be a reasonable choice. On a full-sun deck it will let the timber grey underneath while still looking sealed.
Semi-transparent stain
The usual right answer for decks and exposed timber. It carries enough pigment to block UV while still letting the grain show, and it wears by fading rather than peeling — which means the next maintenance coat is a wash and recoat, not a strip.
Solid stain and paint
Solid stain gives the most UV protection and the most colour choice, and it is a good option for fencing, railings and vertical siding like T1-11.
Paint on a horizontal walking surface is where people get into trouble. It sits on top rather than penetrating, traps moisture underneath, and peels. Vertical surfaces are a different conversation; deck boards are not.
Preparation decides the outcome
Whichever you choose, the surface has to be clean, brightened and dry. Grey, UV-damaged surface fibres have to come off or the new coat bonds to dead wood and lifts with it.
Not sure which your timber needs? Call (240) 981-4472 and we will come and look at it.