17's and more sidewall will offer more protection over 18's. That being said, big enough pot hole will still crush even the strongest wheel. Between those two, id grab the TSW's, should be found cheaper and i like multispoke design.
My advice is to avoid the potholes as best as you can. Keep more distance between you and the cars in front of you so you can spy the holes sooner and have higher chance of avoiding. Knock on wood, i havent bent my RFP1's ones