Use them both, and see which works better for you.
I preferred the boat, as did my younger daughter (3). She liked the wind in her hair, and I liked being outside. We would actually just go for a ride on the boat, and take multiple trips around the lake without getting off.
My wife and older daughter (6) preferred the monorail. My older daugther liked going through the Contemporary.
Only problem for us was that you had to fold up the stroller for the boat.
We never had a line-from Poly, MK, or GF. It was great to be on the boat for the Electric Water Pageant.