I'd go with the MN2, since you've never paddled one.

That weight difference will likely dictate who's in the stern, though the 18' length may mitigate this.  I was once tandemed in a 15' with someone 60# lighter than me.  He tried to put me in the bow, it was an interesting ride.

Heck, if you can convince the Mystic to take the Champlain you can play about comparing these similar Wenonahs.