Dropped my iPhone from about 2 feet high, and it turned off and I wasn't able to turn it back on. I found out my sister had previously replaced the battery with a $5 battery she found online. So we put her battery in my phone just to make sure it was the battery that was the problem (with the battery from her phone, my phone turned on). So I did a little research and a lot of people said that they'd trust a battery from ifixit.com, so I bought a replacement battery from here.
Installation was super easy, and over 2 weeks later my phone is still working.
I think ifixit.com was a good choice!