I have just sold my cooper
It had 16" five spokes and after 14,000 miles I fitted 17" wheels.
The 17" wheels looked much better but the caracteristics of the car changed dramatically.
I have just ordered a new cooper and it will have 16" wheels
so if its looks you want 17" are good
If its comfort then 16" are better
As for road holding there is not a lot of difference
Hope this of some help