In my experience, I have found that 1/200 - 1/400 is the sweet spot to be an ISO of either 100 or 200.
I use ISO 100 / exposure 1/400 on sunny days
If it's cloudy or near sunset I would drop it to 1/200 and have my iso at either 200 or maybe 400. This will provide a little brighter image for the slightly darker conditions.