I'm familiar with all 3. They're 'ok'. I'm not a Merrell fan.
All 3 versions weigh less than 2lbs. The waterproof or Gore booties will add way less than 1/2 ounce.
The vent model is just that, a mesh upper for some breathability.
The Gore version has a waterproof/breathable GoreTex bootie glued between the inner liner and the outer.
The waterproof version has a similar non-branded bootie that Merrell doesnt have to pay a licensing fee on.
Most people can not tell the difference in the waterproof and the Gore breathability. If they say they can, I dont believe them.
Buy an Oboz instead. Either a Sawtooth Mid, a Yellowstone, or Traverse.