A quarter-zip base layer is your best bet when you run hot or ski in milder conditions. The zipper extends down to mid-chest, giving you maximum venting power—way more than a half-zip—so you can dump heat fast during high-output activities like skinning up in the backcountry or hiking to fresh lines. It shines on warm spring days when you're alternating between sweating on the run and cooling down on the lift.
The tradeoff is that the lower collar provides less neck warmth than a half-zip mock neck, so cold air can sneak in on frigid days. Also, the longer zipper can create a slight bulge under tighter mid-layers, though it's rarely noticeable under a looser fleece or jacket.
Skip the quarter-zip if you typically ski deep winter cold or always wear a neck gaiter anyway. But if overheating is your main struggle on the mountain, this style gives you the most temperature control of any base layer top.