Round Column vs. ram with dove tail?
Well If you have to move the head in or out while in the middle of a setup, Which is something that happens quite a bit where I work, (not as likely to happen in a home shop) you would be adding a lot more time to indicate the head back in position with the round column. With the dovetail you would only have to re-establish the Y axis.
On the other hand with a modern Bridgport in order to move the head left or right you have to release the 4 bolts on the front, and they seem to be a weak point, as I've seen them needing to be replaced periodically on the machines at work. It's also a little bit more of a nuisance when tramming the head back in, because when those bolts are loose, they allow the head to nod forward a little, which means you have to go back and forth a few times.
It's also possible that the dovetail version is a little stronger, but I doubt it's anything anyone would notice in a home shop environment.