I've used the City Mini (single and double) at work...They handle well on bumpy pavement but across grass I found them both difficult to push as the small wheels get caught up with debris and drag along.
I don't have any experience with the Oyster but the larger rear wheels should help with handling on different surfaces.
We bought the City Select when DS was born, it has the larger rear wheels and it has been great - I use it every day (it is basically my car!). It is not as compact (when folded) as the Oyster or City Mini though.