I already explained longer range, but I suppose I'll need other details. The Monado's blade is a beam of Ether, which is basically Life Energy/Spirit Energy. Zan Lance, might be able to break through Monado Shield, but it's still a metal sword as far as we know. It's kind of like comparing a lightsaber to a normal longsword. Also, while Shulk himself has never used the Monado to this extent, but the Monado II is the same monado Zanza used to cut the Mechonis; a Moon sized giant, in half. That says a lot about his potential range, although, his in game range is only dozens of meters, which is still much more than Zael's.
Shulk also has more varied sword techniques in general, Back Slash, Slit Edge, Air Slash, Stream Edge, Shaker Edge, Monado Buster, and Monado Cyclone. Zael, aside from his basic sword slashes, only has gale and vertical slice. Shulk's Monado Purge could also have a similar effect to Zael's Gathering Burst, and Shulk's visions could easily be used to counter Zael's best sword techniques. So yeah, it is a pretty close call, but I still gotta vote for Shulk for those reasons.