You should always use the film gamma setting unless you have an external LUT generating box designed to setup your monitor in a particular way. Turning the gamma selection to Uncorrected simply gives you the raw gamma response of the LCD panel without any calibrated gamma function applied. Please note that in order to select a specific gamma response for your monitor (i.e. 2.2 or 2.35) you MUST have the monitor in film gamma mode.

Film gamma is the default setting and uncorrected is very seldom used or needed. Uncorrected is only useful in that it allows an external LUT generating device to setup a monitor in a particular way without competing with the built in LUT normally used by the monitor for proper calibration.