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I would recommend water sprite, hands down. Great for taking excess nutrients and looks very nice floating. It is virtually impossible to kill once you have a few bunches.
I don't think there are better floaters than Brazilian water weed and Pennywort. The Braz weed gives off a mild chemical that's known to inhibit the growth of most species of algae. My Livebearers thrive in both. Both will grow well in subdued lighting.