Factory or after-market brake pads?

I talked to my local mechanic today and asked him how much it would cost to replace the rear brake pads on my car (which I’m planning to get replaced tomorrow). He gave me quotes for two different types of pads: factory replacements and after-market.

The after-market pads would be $25–35 cheaper (total). I’m trying to decide whether it is worth it to pay more for the factory pads or just go with the cheap ones.

I’m assuming that the biggest difference will be the durability and lifespan of the brakes, so I’m thinking it might actually be cheaper in the long run to spend a little more now to get the factory pads.

Can anyone give me some insight into which ones I should get? Save the money or get the better pads?