We don't have a 3670, we have it's little sister, the 3370. (no longer made) that being said, if we would have had the dually when we were shopping, we'd own the 3670 as well. There are a couple more that I've had my eye on, the new 3455 (I think) and the bighorn model of the Landmark Rushmore. You really just need to look at as many as you can, sit in them for awhile and imagine how they would function for what you need. You really will know when you find the right one.
No matter which HL you wind up getting, you simply can't go wrong with this brand. For us, the factory support has simply been exceptional for the almost 4 years we've owned it. Even my repair tech at work was impressed by how well the unit was built, and he has seen quite a few.