Q: Sometimes my hens' waterer gets algae in it--is there a better waterer?
A: Not that we know of. Algae grows in conditions of water with excess phosphorus or fertilizers in it, and growth is encouraged when the water is also in the sun. It isn't related to the type of waterer you use, although it's possible you might get a bit less algae with an opaque waterer, if the sunlight is blocked from hitting the water.
To avoid excess algae, put your waterer out of the sunlight and evaluate the condition of your water. Adding a little vinegar to the water to acidify it can discourage algae growth, but won't help much if your chickens' water gets droppings scratched into it (adding "fertilizer") or if your waterer gets a lot of sun. You also won't want to add vinegar if your waterer is the galvanized metal variety, as that could encourage early rusting.
A last idea would be to switch to a smaller waterer that gets filled and cleaned more frequently, and so doesn't sit around long enough for algae to grow. The artisan waterer pictured above is great for this: it's small for frequent easy cleaning, you can safely add a splash of vinegar, and it's opaque to keep out sunlight better.