Viper, Python, Clifford, Hornet, etc... are all made by Directed Electronics... DEI... it's all the same, just different badging and slightly different remotes and brains. Otherwise, same.
www.directed.com
I've had both Viper and Python... they're both good units... just be careful with the remotes... that's the first thing I've seen go on any two way paging units.
As far as sensors are concerned, either one will come with a shock sensor only. Tilt, glass break, proximity sensors are all extras. A shock sensor is an impact sensor. It will not detect someone jacking your car if they do not generate enough vibration to set it off. The shock sensor's purpose is to warn you if someone has hit or bumped your vehicle while you were away. Also, depending on how it's sensitivity is set, if someone is attempting to steal your car and breaking glass or jimmying your door to get it open, it would warn them away or set the alarm off.
Tilt sensors work from 1 to 3 degrees of tilt. It is installed in a location that is as parrallel to the vehicle's surface as possible so that a minimal amount of tilt is required to set it off.
Glass break sensors are a microphone placed on the dash somewhere to detect the sound of glass breaking and that would set the alarm off
Proximity sensors are microwave sensors that allow you to set a warn away field disturbance and a full alarm mode field disturbance. Mainly designed for convertibles so that no one can reach in and steal something. These are sensitive to hot and cold climates and affect the field of both zones... so they can be tricky to set up.
Hope this helps,
Nick