Don't want to buy something that will keep my sidelined wanting a snowmobile. I would just go snowmobile but I could use some of the other utility of the ATV.
ATV for Ice Fishing
I bought a Polaris Sportsman 570 last yr and used it exclusively on Petenwell the entire ice fishing season, not once getting stuck. I never put chains on the machine either. Should I? I suppose I could but never had an issue getting through any snow. It pulled my one man clam and auger like a champ. I was and am very happy with the purchase.
ATV's are great most years but when the snow gets deep they just are not effective. Chains make a HUGE difference and an ATV with chains will usually get you around fine until it's safe to bring a truck out.
I don't believe either a snow mobile or an ATV is an all purpose machine unless you go the route of the tracks so go with whichever one serves the most purpose for you.