Which tyres should I fit to my Lexus?

I am buying a Lexus IS 300h: I have a choice to fit 205/55/R16 or 225/45/R17 as opposed to the standard 18-inch wheels. Which do you recommend?

Lexus IS300 Sportcross - Tyre and wheel sizes

I plan to replace the wheels and tyres on my 2002 Lexus IS300 Sportcross, because the rims are corroded and the 45-profile tyres give a slightly harsh ride. The existing standard wheels are are 17in...