close, but slim edge to Mountainside
Have traded to both during ski season.....4 times to Summit Watch and 3 times to Mountainside. both are great. Enjoyed proximity to downtown and restaurants with SW, and also convenience of MS's ski-in/ski-out advantage. To me, MS is the preferred resort, but either is a treat. The closeness to ski slopes superceded the proximity to town.
You WILL NOT NEED a rental car....may be a hassle to keep up with one-----if you like having one, no problem, but....the free shuttle buses are simply too convenient, and you seldom wait more than 5 minutes at the most. Even a shuttle bus trip to upscale ski resort Deer Valley only takes about 8-10 minutes.
My pick would be MS by a mere snowflake. If you happen to get a high floor overlooking the slopes/mountain/valley view, you'll think you're in heaven. (Ask for "high floor with pool overlook, overlooking slopes, into valley"---that's what you want----it's a killer view).
The ONLY disadvantage of MS, perhaps, is you may be able to hear the snow grooming machines at night.......it's a faint but grinding-type noise------they seem to run for hours.....a very minor distraction, but I did notice it....the rest makes up for that, by far. Love the resort. smaller rooms only by a foot or two, and not really noticeable. have fun. Whatever you do, try ZOOM, Robert Redford's restaurant next to Summit Watch. Great food. jme