You can have both plants and leaves, and I would definitely recommend both. =) I second being careful about pond leaves, they could contain various parasites or critters you dont want to breed in your tank. I'd get low light stem plants that you can put leaves around. Plants will out compete algae but not bacteria, unless you're speaking of cyanobacteria, and you don't want that in your tank anyway.
Def would recommend almond leaves, banana sprigs and guava leaves!