Paradiso is right by the Pleasure Island boat dock (not West Side), but the PO boat docks at the Marketplace. It's probably about a 10 minute walk from there to the restaurant, or you could ride the shuttle boat from the Marketplace to the PI dock.
If you take the bus, get off at PI stop, which is normally the 2nd stop at DTD.
Sorry, can't say which is faster. I'd lean to towards the bus, since the boat moves pretty slowly and will stop at POFQ on the way (plus getting from MktPl to PI), but the bus also stops at POFQ and MktPl and can also take a while.