Glosso would be the easiest to maintain, just "mow the lawn" or rip some runners out to thin it out. Riccia likes to float and needs to be kept down, it's more of a pain in my opinion. Both are easy to grow, riccia will grow in lower light than glosso but you don't have that problem. Just burry some stems here and there leaving the tips of the leaves visible, it will spread on it's own. Obviously until you have a full tank of glosso, you will need some other plants to take up nutrients, a bare tank with this much light is going to be trouble. I'd use hornwart, duckweed and frogbit, all floaters so they won't disturb the glosso carpet below and they will also shade it a little which will probably help keep the tank clean during startup.
Hope that helps
Giancarlo Podio
Hope that helps
Giancarlo Podio