Personally I did not enjoy the Serenity at ALL, and I really wanted to. The clitoral stimulator is too short for me, and doesn't reach my clit (unless I nearly shove the entire toy in, and then that makes it hard to maneuver). I love the girth of the shaft, but it just didn't work for my anatomy - no dual stimulation for me at all.

The problem here is that anatomy differs from person to person. What works well for me may not work at all for you and vise versa.

The reviews on the Opus and Groovy chick both indicate this is a problem. Harmonia really isn't designed for dual stimulation which leaves the Serenity. While it won't work for some, it's still more flexible than your other options.

The key to successful purchase of a dual stimulator is figuring out if you need one that is designed for shallow penetration or deep penetration. If you feel like you've barely inserted the vibrator into your vagina and the clit stimulator is already pushing against your clit, you may need something designed for deeper penetration.

Based on Indiglo's description of her problems with the Serenity, it sounds like it's designed for deeper penetration. The key will be to read reviews from different people and pay attention to stats like "Insertable Length."

There is also the Gi-Ki which while much more expensive than any of these choices, is adjustable which should increase the odds it will work with your body.