Regular fit snow pants are the most versatile option and work well for the majority of riders. They give you enough room to comfortably layer a base layer and a light mid-layer underneath without feeling baggy or restrictive. If you mostly ride at the resort and want pants that handle a range of conditions, regular fit is a safe bet.
The balanced cut means you get solid mobility for carving turns or cruising groomers, and the moderate silhouette won't catch much wind or drag in deep snow. It's also the easiest fit to adapt as temperatures change throughout the season.
Where regular fit might fall short is if you're a park rider wanting that loose, unrestricted feel, or if you ride in extremely cold climates and need space for thick layers. In those cases, relaxed or baggy fits make more sense. But for most all-mountain and resort riders, regular fit hits the sweet spot between comfort, performance, and style.