Which is better? Both have their virtues: mechanical pumps are very long lived, but you have to crank the heck out of the starter before they fill up an empty carb bowl (common in boats that sit for a while). The electrics are not as reliable (though close, and one can always carry a spare) and they CAN be rigged to fill the carb bowl before cranking the starter.
One important caution: Per USCG regulations your new electric pump MUST be wired through the oil pressure switch, to shut it off if there's a gas leak (that would also kill the motor when it runs out of fuel). Since this circuit also removes the advantage of an electric pump (see above) smart guys add a bypass switch to run the fuel pump before hitting the starter.
Jeff