That is a very general question.
In Toronto (North York area), you will find service from Bell, Telus, Rogers and Fido. You will also find the big name MVNO's like Solo, Kodoo, Virgin, etc.
Generally speaking, you will find the quality of signal strenght the same with any of them. What you need to see (probably) are the following:
1. Reception where you will use the phone (at home or work, etc)
2. Types of phones and price plans
3. Customer service