From my understanding, and feel free to correct me if I am wrong, the wider a tire is the less you will notice smaller imperfections in the road due to the width of the tire being able to cover more road left to right. The taller the sidewall will allow for more cushion when you do hit imperfections in the road due to the ability of the tire to be able to flex more.
With those two points made, the 235 tire would be able to avoid more of the imperfections but the 225 would have more sidewall to absorb any imperfections you do hit.
I am also looking for 17's and will be following this thread to see what others have to say.