matlk14honestlty go look for like a early 2000s to about 2007 skidoo summits or rmks. they can get you back into the backcoutry with some practice youll nearly be able to go anywhere. they run any where from 1000 to 3500. 600 would be alright if you keep it on the trail and out deep powder but 700 and 800 would be the best tool. if your in the market for more expensive sleds dont buy any 900s or 1000s there p.o.s. usually. and i agree take an avy class and make sure u have more than one kid!
I second this. The Polaris RMK is a solid machine. The only thing I have to say about engine size is it really matters how old the sled is. An early 2000's sled that is a 600 would only really be good on trails and some flat powder. However these new machines (especially the RMK) are so light that small cc would do just fine on most any terrain. Now don't get me wrong! there is definitely a noticeable difference between a 600, 700, and 800. I however have easily been able to hold my own on a 600. As for track length, I would say look for a 155 or 160.
If I was to give you one piece of advice, it would be to buy a newer machine. Sleds can be a bitch to work on and you can count on things breaking. Most used mountain sleds have been ridden hard and may have problems that can go unseen to the naked eye. If you do buy used pay close attention to the frame to make sure it is not warped, the engine has good compression, sounds good, and that the clutch is responsive.
Also buy LOTS of belts and always bring one with you, because you will go through them quick.
What's your budget?