Are these tiles "self-spacing", meaning do they have lugs/bumps on the edges that seperate the tiles by 1/16" when butted to each other? If not or if you don't like spacing that tight, I usually try to take my que from other tile elements in the installation. Do you have a liner or decorative tile in this project? If so, does it work better with a tight or a wide joint? Do you have other tile elements that, when laid next to your field tile, work best with either a tight or wide spacing?
I keep 3/16" spacers as well as wedge-shaped spacers in my truck at all times, as they are the most common that I use. Anything else, I usually let a designer or architect specify.
Best of luck,