Isf is a bit more nimble and lighter on her feet compared to the Merc, as for holding value the isf never got replaced unlike the RC that got hammered by pundits and the the LC hailed as the one to have even though the RC was mainly attacked due to not out doing the M4. Unfortunately these critics do have some influence on immediate prices but long run prices tend to balance themselves out. As mentioned previously RC is more modern looking over isf and if it's a coupe you are after it's the next best option... a true Lexus lover appreciates the cars worth so you would probably get roughly your money back (minus petrol and tyre consumption haha).