Best margins for master thesis written in LaTeX
Your question may not be completely appropriate for academia.sx but probably not for TeX.sx either.

Anyway. rather than focussing on the width of margins you can consider the width of the text area. Research (I do not have references at hand at the moment) has shown that around 65 (within the range 45-75) characters per line is optimal. This means that if you switch type face or size, the number of characters will change. Hence the same text area may not be optimal for 10, 11 and 12 pt or conversely your text optimal area will change with type face and size. To some extent, this is built into LaTeX which is at least partly why the margins may seem less than optimal.

So to approach the question of margins, try to select the type face and the type size you want to use and then check the resulting text area size for line lengths between 45 and 75 focussing around 65 characters.

The question of right and left page margins is a matter of simplicity. If you centre the text area on the page the areas will appear the same on all pages. When viewed as a pdf the text will not move around from page to page which can be slightly annoying, particularly if inside and outside margins have widely different widths. So will your text be read frequently in digital format use simple margins, if the print is important differing in- and outside margins may be preferable. Just make sure any printer does not screw up the margins by removing or missing printing blank pages that will result in a shift of left and right hand pages.