my shop only installs DEI systems (viper, python, sidewinder...) as said they are the best designed system the easiest to install and have the best warranty, i also would not put any faith into what ford calls a factory alarm.
viper models i would choose from
160XV -remote start, keyless entry, panic, two remotes, 500' est range, trunk pop optional (no alarm)
160XVL -same as above with up to 1 mile range
771XV -remote start, keyless entry w/ panic, trunk pop optional, alarm with two stage shock sensor one remote with 2 way 500' est range and led's to confirm start or alarm
791XV same as above but with a 2 way LCD remote, discontuned and replaced with the 1 mile 5900
5900 -2 way LCD 1mile range remote R/s, alarm w/ dual stage shock sensor, keyless w/panic, trunk optional,
responder LE - new system with very small and thin 1000' range remotes w/ LED's
by the way if you conti is a 98 or newer expect to spend an extra $100 - $150 over the regular price to bypass the PATS (chip in keys) and you will have to have at least 2 keys for them to program the bypass to the car