The boat ride is short as already stated, but the wait for the boat can be a while. Depending on when you're there, Portifino and Hard Rock share a boat if it's slow. This can really slow down the boat.
I find it's easier to walk.
Also, if you're enjoying adult beverages at CityWalk, you can finish them while walking, no booze on the boats! Security will make you finish your drinks before you hit the actual property of the hotel because they hold a separate liquor/beer license.