Pros
RWD - allows you adjustability and some control when you exceed a chassis's limit of traction.
FWD - the chassis's limit of traction is easily accessible to the driver and once exceeded, easily modulated.
MR - Stable chassis with high traction limits, is also balanced and neutral in most cases.
Cons
RWD - You need to know how to really drive in order to access its advantages as you have to drive beyond the chassis to extract full advantage. For example:- A fully built RWD should be quicker than an equivalent FWD car in most situations. The problem is if you are a novice driver, you cannot access the advantages of the RWD chassis as easily as the FWD's. As a result, FWD cars rule (in certain classes) on tracks where the drivers are not of a certain level, e.g. Sepang as most of us (me included) are not of the requisite experience or skill to fully exploit RWD.
FWD - Once you have exceeded the chassis's traction limit, there's not much you can do. Back off the gas....that's about it. Don't get me wrong, they are still deadly fast esp the new gen FWD's with their LSDs and trick suspension geometry. Problem is and this is for certain parties only, is that FWDs ultimately lack the drama and emotion that comes with on the limit driving. Its like a 9 out of 10, a very good score but not the "perfect" score.
MR - The deadliest of the 3 (Bar the RR layout). Super sharp turn in, neutral through the corners BUT (dependent on the setup) get it wrong and it WILL spit you out like nothing else. You get adjustability, agility and (most) of the time, supreme stability. The trick is again being able to drive beyond and predict it on the limit behaviour. Master it and nothing comes close.
My personal preference is for the MR but given a choice and on most days...4wd takes the cake. No need to think, just drive.