It is really hard to compare the two. They are entirely different and each appeals to folks in different ways. There have been a lot of very good statements made. I have a 2006 Airstream that we purchased used in 2009. Buying new was out of the question for us and we were able to get a pretty good deal on the used one. It is now 12 years old and we would be able to get very close to what we paid for it 9 years ago.
Airstreams are small and that is a huge drawback for many. Mine has almost NO exterior storage. The inside is fine and the curved upper cabinets are not problematic as some would say. There are no slides and the cost is hugely discouraging. But, after 12 years the original home quality plumbing fixtures still work perfctly, all the doors close and the drawers are still functioning like new. My Starcraft white box that we bought new didn't last a year before stuff like this started to break or cause problems.
I would second the suggestion about the Arctic Fox family of trailers. I have been impressed with the build quality in these. Don't have any experience with the Lance.