IMHO
Buy TOAD, they are insurance approved (when fitted by a dealer), they are ultra reliable(mine is over 3 years old and survives lots of fairly severe off road use) and are dead easy to operate.
They have the usual range of accesories(mine has a 2 zone microwave sensor being a soft top, and so has pre-alert)
Some alarms(like clifford) are great if you want a whizzbang job that starts the car remotely, opens doors/boots etc, puts lights on so you can find it in a carpark, but they are pretty complicated.
Mine has a 2 button fob, works well, and has NEVER falsley gone off in the night(very important consideration)
:D