Rubber grips are the most popular option for good reason—they're the best all-around choice for most skiers. The textured surface gives you solid grip security even when your hands get wet from snow or sweat, and rubber provides decent insulation to keep your hands from freezing on cold chairlift rides. It also absorbs some of the shock from pole plants, which adds up over a full day on the mountain.
Rubber is especially well-suited for all-mountain and general resort skiing where you just want something reliable and comfortable. The main downside is that rubber can degrade over time with UV exposure, so if you store your poles in a sunny spot, you might notice wear sooner. Quality also varies a lot between brands—a cheap rubber grip won't feel the same as a well-molded one.
If you're primarily skiing resort runs and want a low-maintenance grip that performs well in most conditions, rubber is tough to beat. Just store your poles out of direct sunlight when the season ends.