Biggest disadvantage to a quad is cost. But if you want one vehicle to do it all, a quad on tracks would be it.
Snowmobiles are inexensive, and work well most of the time, so use it if you have it. But rigging gets to be a little more challenging when you want to dual purpose a snowmobile. Then some of the accessories are hard to justify mounting on the sled, when they will be in the way for trail riding. A sled also has a range advantage.
Nice thing about a quad with tracks – if you go on a multiple day trip, and there is not enough snow for the snowmobile when you pack to go – a quad on wheels can become useless when it snows 20+ inches while you are on your trip. quad on tracks works for bare ice, or deep snow.
But they are expensive.
I like having one vehicle that I can rig with auger carrier, rod holders, drop baskets, electronics etc so everything is convenient and ready to go. Moving equipment from a quad to a sled, and back again gets frustrating.