Whatever it is... get a pager alarm... if someone touches my car, it tells me... if someone opens my trunk, it tells me.... and something with dual shock sensor... so when a chipmunk decides to sneeze you alarm wont go off..
Other than that... whatever brand has those functions, I would say buy it... mine is an Ultra-Start (it is also a car starter with many features that i like here in Canada).
If you really want to spend the cash, get a digital compustar.... supposed to surpass the 1/4 mile range (my ultra is a 1/4 mile, and was a bit cheaper... so thats why i opted for the ultra)
hope that helps.