These are the calibration settings that we used for our review of the Vizio M Series 2016. These settings will work well for everything except for video games. For gaming, you will also need to enable 'Game Low Latency,' and you should also use HDMI 5 to get the lowest possible input lag.
Start off by choosing the 'Calibrated Dark' picture mode. If you are in a bright room, or find our settings too dark, increase 'Backlight' as much as you want. It won't mess up the colors. Don't touch 'Brightness'. For 'Sharpness', leave it at 0 for 1080p and 4k sources to prevent any over sharpening. For lower-quality content, like DVDs or SD channels, you might want to increase it a little bit.
If you find the picture a bit too yellow and dull, change 'Color Temperature' to something colder. If you don't like to have the screen consistently changing luminosity depending on the scene, or if you see some blooming around bright objects, turn off 'Active LED Zones'.
If you want to enable the soap opera effect on movies and other 24p or 30p content, increase 'Reduce Judder'. On 60p content, you will instead need to increase 'Reduce Motion Blur' to create the motion interpolation effect (and set 'Reduce Judder' to at least 1, or else it won't kick in).
Update 05/30/2017: The M50-D1 and M55-D0 cannot perform motion interpolation, and so do not have 'Reduce Judder' or 'Reduce Motion Blur'.
If you see too many artifacts or too much noise, enable the noise reduction features. Keep in mind that these soften the picture, so don't turn them on for high-quality content.
The following are the results of the white balance and colorspace calibration on our unit. They are provided for reference, and should not be copied as the calibration values vary per individual unit even for the same model and same size as the TV we reviewed due to manufacturing tolerances. If you want to try them you will need to enter all values shown, as all of them are active at the same time. If you end up with worse picture quality, simply reset them to the default values.