I'll attempt to explain the difference. This is a generalisation. There's many different combinations and variations:
With a torque sensor and torque control system, the harder you pedal the more torque you get from the motor, so It multiplies your torque. The multiplication factor depends on a setting on your control panel. The power is easy to control, but you don't get enough power if your legs get tired, so better for people that don't get tired legs.
A cadence sensor tells your controller that you're pedalling so the controller gives a fixed amount of power when you pedal. The amount of power is selectable from a control panel. You can still get maximum power with tired legs as long as you can turn the pedals.
The expensive bikes often use a combination of both systems.
There's many types of controller, which is the box that controls the amount of power to the motor. Exactly how they give it depends on algorithms in their software, so it isn't enough to divide into two catogories of TS and CS. Trying one bike with a TS and comparing it with one with a CS isn't enough. There's some lovely bikes with CS systems and rubbish ones with TSs, and vice versa.
One final consideration. The Chinese control systems, whether TS or CS, (but mainly CS ones) use two principle modes of power control. Some use speed control and some use torque control. Speed control means that the controller aims for a set speed, which is selectable from a panel (though it doesn't tell you the speed) and uses its own power algorithms to keep you at that speed. Torque control, gives a fixed amount of power regardless of your speed. The speed control systems give a more fierce start, but have the advantage that they self-adjust the power for hill-climbing. Torque control gives a gentle start, assuming that a low level is selected for starting, and so feels better, but you have to turn up the power when you encounter a hill. These modes are not dependent on whether you have a TS or CS. Don't get confused between torque sensor and torque control. Though not so common, you can have a torque sensor and a speed control controller.
The only system that I'd avoid, because the other systems are better, is the ones with only one level of PAS (no control panel) because they give you full power whenever you pedal, which is not necessarily what you want.
Whatever system you have, they all work, and you soon adjust to them.