The slush really wasn't much of a problem where we used to live in Colorado. Most of the time it was between 30 and 60 below zero.
It was usually only a problem in the springtime (May) in the afternoon, and one crazy time in March when it rained on top of three feet of snow.
stevelyn probably knows a lot about snow machines - I can't remember if he's on APS or just THR 
He's probably out chasing a drunken indian on a snow machine right now 
Tallpine........I'm in tears and my sides hurt right now.
I chased a few when I lived up on the Yukon, not so much out here in Aleutian Hell since the snow don't last long and there are only about three I'm aware of now. Our DUI vehicle of choice in AH is the 4-wheeler.
Snowmachines are a primary mode of winter travel further up the AKPEN and in the villages where it's colder.
Snowmachine preference for me is dependent on what I'm using it for. For trapping and work on tight trails and deep snow, nothing beats a one-lung Yamaha Bravo and it's powerful enough to tow a sled.
For traveling and general tooling around though I like Polaris. They seem easier to control and more comfortable. They are easy to start when the temperatures are colder than -20 F, and they run well at those low temps. I think Polaris tunes the fuel/air to compensate for the higher density of the colder temps because they seem to run a little rich when it gets above 20F. I'd go out and start mine and my GF's machine at -40F and it'd crank right over on the second pull and sit there and idle smoothly. Had to throw a tarp over it so the track could warm up though.
There isn't anything wrong with the other brands, but like anything else they have their quirks.
Arctic Cats don't like to run very well below -20F although EFI changes this because you don't have to deal with carburator jets. The brain box does the fuel/air.
On some of the faster ACs, I've felt like the machine wanted to fly away with me once I got up past 60 mph. Yamahas are fast, but they are heavy and get stuck easily on unbroken trails.
Most of the machines out in the Yukon/Koyukuk villages are Polaris followed by Yamaha and rounded out by Ski-Doos. I've seen very few ACs out there.
I have very little experience with Ski-Doo, but friends who have them swear by them. I've never heard of them being problematic.
If you are going to get a used machine make sure you check the sliderails on the suspension. These are plastic rails underneath that the track slides over as it turns. The snow acts as a lubricant when you're moving. That's why the comment was made about slush. Wet slushy snow doesn't work as well and you wear the rails out faster. Also the reason I prefer air-cooled engines to liquid cooled. Besides liquid cooled machines are heavier. Heavy machines are a bitch to unstick.
Make sure the drive wheel and clutch are in good shape as well as the drive belt and always carry spare belts and sparkplugs.
If you are going to be in deep, powdery snow, breaking trail or even wet snow, get a machine with a 136" or longer track I like the 144"s. You can also increase your floatation by putting a set of ski skins on the skis. They increase the width and length of the skis making for a bigger footprint which spreads the weight of the machine out better. Not an issue when under power, but if you stop in soft snow you won't sink and you can get moving again a lot easier without the track digging a hole to bury you in.
As far as engine size, I rode up and down the Yukon River on a 440 Sport Touring and never though I needed more power or speed. Even in rough ice and breaking trail. Plus once you get up past 500cc, you enter into the liquid-cooled realm. I could make a 223 mile trip on a tank of fuel. The new 4-strokes are probably even better if 4-stroke outboards are any indication.
Be aware that those things can kill and cripple ya quick. There are more folks than I care to count that I knew personally that were killed and seriously injured on them and from them mainly due to stupidity. Some of them I had to bag myself.
