Here is the straight up skinny.... Viper, Python, Clifford, Avitol, Express and a few others are all owned by the same company. All of them are Directed Electronics products. The boards and internals are virtually all made the same. They are all a quality product of and in themselves.
The true difference in a quality alarm and one that does not work rests 90% on the installation.
How well it works: Does it pick up all the points of entry? Does it respond well at a good distance? Does it work every time? Will it last? All of these questions are directly to related to the actual installation. Did the installer solder all the connections ore use but connectors or did they T-tap? Did the installer garb the wires and info it needs in the right spot or did they get lazy and go for the easiest spot, which sometimes is not the same things. It can make a difference where you pick up ignition source, constant power and door triggers. For example, many many systems have the ability to sense voltage sensing. They monitor the main power input that is connected up and if there is a change ion voltage, it will trigger the alarm. Many installers will use this as the way to trigger the system if the door is opened. This is not a good way to get that trigger and will inevitably cause false alarms. Another is example is using T-taps. very common in the budget alarm install. the t tap will work for a short while but again, inevitably will cause issues. Consider that a car is constantly vibrating and shifting and hot and cold and hot and VERY hot and Very cold and vibrating. It is a rough environment. The best method in my opinion is always going to be good tape and solder. A good quality electrical tape will work amazing. Also Solder and heat shrink, though on the larger wires that are connected to like the ignition, etc, cutting those wires in half and then re soldering can be tricky.

the next important thing is prepping the alarm. A good alarm install, half the time is spent getting the alarm ready to go into the vehicle itself. When I install, I know where the connections are going to be and tape all the wires up in black tape all together so they are running together to the same location. This is how the factory does it, this is how I would do it. It makes for a little longer install, but it makes for a cleaner install. I figure out all the wires running to the kick panel and send them all there. I also run all extra wires not being used to the kick panel, so that in the future, if I need to do something with those inputs and out puts, they are accessible. That leads me to the last thing. Cleanliness of the install. When you look up under the dash, you should not be able to tell what wires were from the factory and what wires were from the alarm. It should all look the same. It should all be taped the same and the brain hidden. No jumble of wires pointing directly t the brain and an easy easy easy bypass.
Where do I draw my opinion? I did this for a living for over 10 years. Started out working at Dalworth CB and Car Stereo, then moved to a shop called Autotronix Custom Car Audio and then to DFW car Stereo. I loved doing alarms, they were my specialty and in every alarm I did, I would try to do the next one better than the last. I would take pride in the work I did. With an alarm, I can do virtually anything that the cars did on its own electronically. Start it , stop it, roll the windows up and down, pop trunks, remote winch, put tops up and down, turn neon on and off, remotely move amp racks. With a re'ay or two or 5 it can be done!!!

So this is my first post here, and you can take it for what it is worth. But I believe ask any good installer and they will tell you the same thing.