Shannon Ashley, I’m writing a story about a threesome I just had right now. Rose has a much bigger fan-base and Sensual Enchantment is more of a niche publication. MyErotica is more for the down and dirty erotic story and SE tends to be about the story that happens to have erotic elements, to explore the sensuality, connection, emotions and magic of sexual connection. Which ever works best for your story is what you should pursue.
I personally adore threesomes and write about them often. They are one of my favorite sexual things.