First of all my $. 02 on the brand to look for:
I personally would stay away from Clifford. I'm not saying they make a bad product, but I have installed a few Clifford alarms and have not had a good success rate with their products (bad alarm brains, some right out of the box). This seemed to be on some older Clifford models, I think the new ones are better.
Viper does make a nice alarm, but if you plan on doing the installation yourself viper is not for you. I'm pretty certain that Viper can only be installed by an authorized retailer. You may find a dealer that will sell you one though.
Alpine makes very nice alarms. I have installed a number of these and was very happy with the installation and available features.
Finally, I also really like the Code Alarms. If you will be doing the install yourself, the Code Alarm directions are, by far, the easiest to follow. The Code is also very nicely priced when looking at the features it has. IMO the Alpine has a slight install advantage if you know what you are doing because it has more built in realys than the Code Alarm, but the Code Alarm wins hads down if you need a bit more step by step instructions.
As far as the why have an alarm at all comment: Yes I agree that a more experienced thief will think nothing of this, and will diable the alarm very easily, in most cases. Hiding the siren, power supply line, and alarm brain will help make the alarm more effective, and providing a backup battery/siren will also increase it's effectiveness. I'm a believer in the statement that "the alarm is only as good as it's installation. " Yes I agree, if an experinced thief walks by and sees you have an alarm, he won't even care.
As for the unexperienced thief, an alarm, IMO, will make a difference. Plus you typically save a few dollars on insc.
For me the alarm adds a bit of peace of mind in my not too highly crime stricken town. The alarm was also installed because I wanted keyless entry and a remote starter (Code Alarm Sure Start LX).
Sorry so long, take my opinions for what you think their worth.
Ryan