Which o2 sensor is the best buy?

Before you purchase that expensive O2 sensor, be sure that this is what you need. A scanner with live data can observe the activity of the O2 sensor and tell if it is actively switching. The more it switches, the better. It has a threshold of 1/2 volt and switches above and below this setting. Above 1/2 volt and it tells the computer to go rich and when it goes below that 1/2 volt it says go lean. This is interpreted by the computer and it controls the fuel injection by milla seconds of on and off time. So in essence, the O2 sensor has to do with fuel management. The best sensor is the OE= original equipment and sorry to say is the most expensive. Hope this helps.