I don't recall reading very many critical comments about Casita's construction, but I do recall seeing comments about Scamp's... such as, how they seal the top vent, and there was a guy whose plumbing was installed incompletely. Not saying that Casita is perfect, but I read less negatives about them on this forum.
The Scamp will feel a little more roomy due to the wider aisle, IIRC. And jalousie windows
are a big plus.
Does Scamp still locate the thermostat right over the bed, where it can get banged easily by sleepers?
The insulation difference probably will be negligible, because the thickness of the carpet probably offsets the lack of that thin layer of insulation.
Like Norm said, floors rot from the top. And if you do get water leaks
or from plumbing, you don't want it standing trapped against the wood... does Casita put in a drain anywhere on the bottom? I don't remember.
A Casita 17' with front bath will have a hitch weight
that most likely precludes the use of any vehicle with a 350 lb hitch weight
limit, where as a Scamp 16' will not. Whether this matters to you or not depends on what you might want to tow with, now and later.