I have a 351W and went through this debate a few years ago. W's are much less tempermental in getting everything just right. C's have more potential but only if you have a degree in the engineering of air flow. Proof of that is the fact that the 4V heads are only good for all out racing and RPM levels that would keep you tethered to the gas pump.
W's on the other hand will give you a very streetable 400HP with good performance across a very usable RPM range. add that to lower cost and greater availability of parts and you have your answer.
The C engine had lots of potential but even Ford shut the line down because it would be too expensive to continue development when the W would give you so much for so little.
i agree with the above post about w and c... if you got the money and are only making a drag car go with the cleveland. but if you want a streetable car that is cheaper go with the windsor. there are alot of different packages out there to create horsepower with the windsor, the best way to go is stroke it out to a 393 or 408. my set up is very nice also with out stroking it. mid 13's right now but itll be low to hopefully high 12's next year after the new 4.11 gears and aod change. and it wasnt overly expensive compared to what i have heard of others spending to get the same times.
You obviously have not driven a tuned 351C-4V quench chamber motor. This thing rocks! Sure it builds its power above 2000 rpm, but who doesn't leave a stoplight with serious intentions above 2000 rpm anyway? It will still cruise well at 1000 rpm even with a mild cam. This motor keeps pulling hard all the way to 6200 rpm and would leave all but an expensive aftermarket laden Windsor behind at about 70 mph.