With enough research, you'll find (on this site and elsewhere) that common experience is the Carter W-1 is somewhat cheaper to buy and rebuild, and are generally considered to be bullet-proof. Carter refined this carb through the years, with the final version starting in 1941 - I think it's the 483s - addressing the last few minor issues with the W-1.
The Rochester -as from the factory - gave a few more horsepower, but are widely known for being leaking, messy monsters. I think Carbking has said that he used to routinely have to put them in a jig to re-flatten the flanges. Other than the mess, I haven't heard that they're unreliable. I think the kits for them are reasonable as well. And they're plenty of them out there - they often show up on the earlier trucks as replacements for the Carters.
Here's carb king's page for the W-1s.
Carter W-1 Hope this helps?
-Michael
