The Novotel would be closer to the Marais whilst L'Echiquier is closer to the Opera and great Boulevards, but personally I like l'Echiquier better in terms of style. The location is not seedy, but it's a big city so obviously a few streets up or down will be more or lesspleasant. Les Halles has some dodgy people around in some parts in the evenings but is conversely very central and has plenty of enjoyable pedestrian streets around.

Personally, I'd say the best way to come from CDG to L'Echiquier is the RER to Gare du Nord then walk (about 10-15 minutes). If it's many of you or you have lots of luggage you can indeed take a taxi. Taxis from Paris airports are fixed price 9and Uber essentially matches them) - plenty of info in the France travel forum on that front if you need details.