Ive always prefered Orion myself. yes its a lil pricey but the sound modules are the best softsynths ive come across in a long time. The 303 sounds like a real TB.. even better than rebirth (which is now free)

As for external control, Orion is much simpler to build with and wirks great with Acid. Been a while since i twiddled some knobs.. lol time to whip out the RS7000