Hello and welcome to the forums
They both have pretty much the same spec,so you can't go wrong with either but I personally prefer the ASUS one because of having an overall better build quality along with a slightly faster GPU
The Dell XPS 17 is "Item condition: Manufacturer refurbished" In other words - used.
It does have a warranty (or what's left of one) "1 Year warranty till 14/2/13." (that's not a 1 year warranty the way I figure things).