First question I'd have for you is how old your tank is. Usually you need a minimum of 6 good months before you introduce an anemone. You will also need some higher lighting than a typical FOWLR tank has been fitted with.
Ritteri's will host Occelaris but is a harder anemone to keep and I wouldn't suggest it as a first anemone.
Long Tentacle's will also host Occelaris and could be housed in a smaller aquarium (30 gallons or larger), but they can also get pretty big (up to 20") and need 4 inches of sand in the bottom of the tank.
Giant Carpet's will host Occelaris and can also be housed in a 30 gallon or larger aquarium but can get very large. These also need sand substrate and are a difficult anemone to keep. Also keep in mind that not all carpet anemones are natural hosts to occelaris.
I am not an expert on anemones, but if I were you, I would probably stick to the long tentacle anemone because they are easier than the other two.