Even if AST and SCH pull more DPS, WHM wins dungeon mowing with assize alone. Though this is more due to preference. That instant 300 potency with no dmg reduction regardless of number of targets, and also respectable range is just too good, and feels good to use and weave between gcds. If you're like me, and enjoy being a little too close in melee range for comfort, Assize is like the most yummy pudding ever.

So I would just take the healer you feel the most comfortable with. For me it's usually WHM because on top of my love for Assize, it's a more basic healer that doesn't have to micro manage anything.