It depends on the look you want for your deck - do you want the wood to show through or be a solid color? Either way, it is a good idea to also use a water seal product on top as well.
Semi transparent looks better but will need to be redone after a couple years but depending on your weather. If it rains a lot it will be needed more often
Anything that sits on top will show wear and peel/flake. This will cause more maintenance issues long term.