As alluded to by WillTravel, Novotel hotels tend to be of a more consistent standard, and generally in the 4* rating. For the Mercure hotels, those at the top end of the scale are usually branded as Grand Mercure hotels - there's much more variation amongst Mercure's than Novotels. Those at the lower end of the scale used to be called Mercure Inn's, but I think they've all been rebranded across to the All-Seasons brand now - they were generally in country areas, rather than city areas though.