The only product that works for my waterline is Loreal HiP's cream eyeliner. I dip my eyeliner pencil into the cream, dab it on a paper towel to remove any clumps, wipe my waterline with a CLEAN finger to remove any wetness, and then draw the line on. I put my eyeliner on at 7:20 AM, work all day until 3 pm, hit the gym, come home around 5/6 pm and I still have the product on my waterline. It does fade slightly throughout the day, but it doesn't wash away like all the other products I've used (I have really watery eyes).
(Note: I've never tried MAC's liners so I can't compare it to those).