A picture is worth a thousand words.

I belong to the Rounder's Forum, a group of riders who ride in extreme climate conditions...as well as when the more sane riders are out too. One of them has a Ural and takes it up into the mountains in Colorado when the snow is several inches deep. There's a trip thread also about taking a Ural up to Alaska that is in progress right now.
The Ural can go just about anywhere. When you need more traction, you just flip a lever and you get the sidecar wheel engaged too.
The nice part I would think about getting a Ural, is that while it is a dated design, it is also a design that has had the bugs worked out. Any other kind of sidecar rig would be something where you'd be trying something never done before.
There are some bikes out there that are just magnets for people to want to know more about. Stop at a highway rest stop or a gas station, and someone will want to strike up a conversation with you. The Spyder Can-Am is one. The Ural is another. One looks like it is from the future, while the other looks like it is from WWII.
Chris