Spec wise, there isnt much in it really as the F Sport has bigger alloys and stiffer suspension along with the exterior and interior treatment.
Essentially I chose the F Sport as I prefer the seats, the looks and the alloys. Both trims handle well but the F Sport is better. Personally I don't find the ride stiff at all, certainly nowhere near German hard. It does get caught out with potholes though and will thump if you land in one.
As for advise, generally just normal used car advice. These things don't have any common issues. Main things would be leather wear on Luxury models, check servicing as they should be 1 year/10k miles or 1 year/12k miles. Apart from that, nothing stands out.