I think microalgae is the better option because micro algae is the waste product. It creates eutrophication in water. Waste to biodiesel is the allways better compare to all things (plant products, vegitables etc...)
Yes,otherthan alge there are another option that you can be used. Bioethanol is a one way. However, considering the avilability and biodiesel yeild, alge is prefered over othars in my opinion.