Snowmobile or 4 wheeler?
Both will work for ice fishing. Snowmobile works better in deeper snow. Trail riding snowmobiles is a bunch of fun, but you can't plow your driveway with one, or pull a trailer, or drive it in the Fall.
No right or wrong answer, just depends on what you do more of. For me, it's snowmobiles. They get me out on the ice, and my kids and I have a great time on the trails.
I'm still holding out for a deal on a 4wheeler from my buddy, so I might end up with both by next year. ;)
One thing I quickly learned, is that the snowmobile doesn't have as many CARGO CARRYING options as a 4wheeler. I'm curious to see how guys setup their sleds to haul augers/buckets/shacks/etc.
Now back near my house an ATV would be fine most years, I just don't fish around there as much as I used to.