Which O2 sensor is more likely to go out?

What is your question?

My check engine light is on and I finally determined is was the O2 sensor. (O2 fuse keeps blowing. Engine light goes off every time I replace it and pops back up when the fuse blows again) I called auto zone to get a quote on the price of the part and they informed me there are two in my vehicle, an upstream and a downstream. Which one is more common to go out in my car? (if I was informed wrong or my information is incorrect, please steer me in the right direction.)