Serveral factors effect your choice.

1. Do you have similar system installed.
    If you do have the system, means either you don't need pay equipments fee or installation fee, will lower your cost.

2. Do you have phone system?
    Remember VOIP phone is not supported by almost all monitor center.
    You need have a Rogers/Bell landline phone be used to report alarm.
     If you really don't want to install landline, you still have 2 options: one is install GSM module, the advantage is you don't worry about the thief cut your cable wire (can't report if line is cut), but most cost, GSM is about $150. Another options is self monitor.

3. Which monitor center is good for me?
     Actually their service is exactly same. Their service rate is different only. I recommend Lanvac.
     Lanvac give you multi-language service support.(English/French/Mandrin/Cantonese...), free email notification, and no contract..
     ADT only english service, need 3 years contract.
     Counterforce have 3ry party language tranlate.