I went with Scorpio. Bought it from a guy on Ebay who sells them cheap.
Came with all the modules including the perimeter sensor, shock and movement, ignition disable and accessories. Don't remember how much I paid for it but I think it was $200 shipped.
Before that, I used to have the Gorilla. Don't like it. Only has the alarm but everyone can turn on the bike.
An advice, use a disc lock as an add and get a nice insurance. Those three things will give you peace of mind.
I had the Gorilla, with all the bells and whistles, for a number of years until it crapped out on me. The Scorpio is much nicer and that'll be my next replacemet. They ain't cheap and you'll get a lot of varying views regarding thier effectiveness. If some professional theif really wants your bike NOTHING with stop them. However, for more practicle everyday scenerios, I really like alarms as a deterrent. If you leave your bike in areas of concern (hotel parking lots) it makes a big difference and gives you peace of mind while you sleep. In your case, it will keep people from sitting on it (with a perimeter sensor or a tilt sensor). I look at it this way: Anything that will make someone else's bike appear easier to steel, will keep my bike in the parking lot till morning. Sorry for the other guy that did less to protect his and made his an easier target.