If your car had a cat2 immobiliser and you wanted to beef up its security and you had enough brass to get one but not both which would you choose - a cat1 alarm or a Tracker??
Cat 1 alarm myself, if they can get in it, then all they have to do is get it out of sight and remove the tracker, and ive heard of tricks to render those useless anyway, if its as hard as possible to get into, its less likely to go walkies, an even if they do get into it a cat1 will go off when they breath on it, a quick motor will be gone tracker or not, an could get ruined while being chased down by the rozzers.
I say a cat1, maybe a rottweiler on the back seat just in case lol
also bear in mind once its gone it could be a fireball before the plod turn up anyway