I have tried both the Aneros Helix and the Aneros Progasm (regular, not Ice, but they're nearly the same). If I had to choose, the Progasm is a bit better unless you're well practiced with prostate stimulation. Being a bit bigger, it's easier to hit the right spot, and the ball-shaped tabs are more comfortable than the original Helix.
The Helix Syn is pretty similar to the original, though it should be more comfortable due to its silicone layers. That being said, it disallows use of silicone based lubricants, which I found to work best with passive prostate toys like the Aneros.
If I had to pick from your three choices, the Progasm Ice would be my first pick, followed by the Helix Syn.