With as much might as a captain has, by slotting a shield, you will easily be sitting at 20% block, with close to a 40% total BPE score, so survivability will increase dramatically - at least, that's the numbers I see when I slot my shield + healing 1H sword.
As far as stats go, the shield will give you far better stats (and more controlled stats), and you will (most likely) see a percent or two increase on outgoing healing by going sword and board.
However, you will sacrifice DPS (not that ours is anything to write home about anyhow).
At the end of the day though, it comes down to how you want to play the captain, and I do not fault anyone for choosing a shield to heal or tank with.
Maley Oakensage, Captain of Elendilmir
Alas Elendilmir, may you *jingle jangle* forever in the Forgotten West