Would you not get a reputable alarm company/installer first and then talk to them about the options? All types of systems out there so really you need an expert to advise.
My advice is to consider what features you would like in a system first and then see whats available. I recommend getting one with a GSM box attached, this means you can contact the alarm, switch it on/off remotely using your phone (very handy if for example you need to let a tradesperson in while no one is there or a cleaner, for example), it will contact you if your alarm is activated, you can check on the alarm status at any time. A fantastic feature.
It's possible to get a lot more, online access, ability to connect to internal and external lights, etc - it really depends on your budget. The GSM box though is fantastic particularly if you are away from the house a lot or the house is idle during the day.