Depends on what you want from the car, if you enjoy simply being wafted along in comfort and not prone to hard driving along twisty roads then the LS400 is hard to beat, the V8 engine is superb and I found in mine the mpg can be surprisingly good, in fact not much different to my current Lexus (IS300Sportcross) which has the same 3ltr engine as the GS. Can't comment on the GS itself as I have never driven one.
I would certainly buy another LS400.
Good luck with your search.