I like duckweed...there, I said it! The stuff requires no maintenance, grows like wildfire, and is easy to control by scooping out as much or as little as you want with a net. Every time I remove a couple handfuls from a tank I am removing nitrates and other nutrients. It's one of the best algae controls you can have, simultaneously outcompeting the green scourge and also shading it. It provides a sense of security for skittish fish, especially surface-dwelling species like Butterflyfish, Hatchetfish, etc. It is also an easy-to-use addition to any homemade gel foods you may decide to make for your fish, especially if you are feeding herbivores. Got reptiles? Many turtles love it, and iguanas and other herbivorous lizards inhale the stuff.
I occasionally have die-offs, and even the odd tank where the stuff just won't grow, but generally speaking duckweed is bulletproof. I haven't any idea of how relatively effective it is in utilizing and trapping nitrate, but the simple fact is that I can remove more biomass in the form of duckweed from a typical tank, on an ongoing regular basis, than any other type of plant I have ever used, aquatic or terrestrial.
I prefer Giant Duckweed (used to be Lemna major, not sure what they are calling it nowadays), which is about twice the size of the common variety (Lemna minor) and to my eye much more attractive. L.major seems able to outcompete and eventually replace L.minor in my tanks, with the help of some selective culling.
People complain about how onerous the task of removing duckweed is. I don't get that at all; just scoop it out, easy-peasy. The only time it becomes troublesome is if you decide for some reason to completely remove every last trace of it; good luck with that.