One of the pros of proportional representation is that it breaks you out of a two party system. If for example you are righ wingish but don't like the present main right wing party, you can vote for another right wing party that you find more acceptable. Same thing on the left. It would take a lot befoire a right winger would vote a left wing party (or vice versa) because of his disgust at the present right wing party. So there is generally little voter mobility outside of the center ground. In proportional representation, the parties need to stay on their toes much more and do what the people want as there are always smaller rival parties ready to pick up the disillusioned voters.
The downside to that is that no party ever gets enough votes to form a government alone so you get coalitions, and coalitions mean the parties have to throw some of their promises out of the window to form a coalition with a party that promised something different. Also, most coalitions tend to be center-left or center right so the center party is almost always in power and has kingmaking powers. In many European countries you will thus find that the political center is where most of the corruption is.