O2 Sensors

Are the Universal o2 sensors just as good as the OEM types? I am trying to save some money as the o2 sensors are expensive for my 1997 LE V6. Are the unviersal o2 sensors difficult to install? I have some automotive knowldge but have not changed an o2 sensor before.
My final question is should I change all 3 at the same time, I'm not sure which o2 sensor is bad?

Don't use a universal HO2 sensor. Find out the part number you need from a Toyota part department with your VIN number and get the correct part. You don't have to buy it from Toyota, just get the right part. Some cars have HO2 sensors and some have Air/Fuel Ratio sensors. They are not interchangable.

http://www.autoshop101.com/forms/h37.pdf

Just replace the bad one. How do you know you need a HO2 sensor? If you got a code from the computer, then it should tell you what sensor is the problem.