Unfortunately much of the Pixel's camera goodness is built into the software, so switching to a different app will likely result in a decrease in quality.

@KingsleyM Why are you not able to disable Motion Photos in the settings? That works fine for me on both my 4a and 5. Or is the issue with disabling the Motion Photo playback in the Photos app?

Selecting a frame from the Motion Photos video clip will be at a lower resolution by design - that's the only way that the video could be embedded in the resulting PNG without dramatically inflating the file size. The tradeoff is that if, for instance, your subject blinked when the photo was captured you may be able to salvage the moment by using the lower-resolution still captured just before or after you pressed the shutter. A smaller photo is probably better than no photo at all.

It's been a long time since I've had the Camera app crash or hang on me. In addition to Force Stopping the app, you might consider clearing its cache and data in case something might be corrupted.

 

Did clearing data for the camera app help at all?

Why do you want to disable the motion photos? Knowing more about what you're trying to accomplish might help us to better understand what exactly isn't working as expected.

 

Even with Motion Photos enabled, you still capture the still shot at full resolution. You don't have to pick one of the lower resolution versions offered.

When viewing the image in the Photos app, just tap the pause icon at the top right of the screen to disable the animation.

Sharing the image will always be done at full resolution. There is no need to export one of the limited-resolution frames unless you want to.