I've been down both the Snake River outside of Jackson and part of the Colorado River in Moab in inflatable 2 person kayaks.

I think the inflatables are more stable for a beginner than a regular kayak or canoe. They are less likely to tip due to the sides being inflated. But you also should plan on getting wet if you're in one.

They aren't going to be more durable than a hard skin kayak. And a good one won't be any cheaper than one of those "sit on top" type kayaks (which are fine for kids in flat water, but shouldn't ever go down a river with any kind of rapids, in my opinion.)