Coq D'Argent is full of city types as mentioned before, especially during the week. Weekends may be slightly different but not sure. Very quiet surroundings though at weekends so depends on what you are looking for. They have a nice roof terrace which is good when the weather is good. Food is good too.
Not been to Les Trois Garcons but heard good reviews.
A fantastic French restaurant which doesnt get the credit it deserves is Pied a Terre on Charlotte Street. Michelin Starred restaurant, nice central location. Fantastic food and usually good service. They do an amazing 8 course tasting menu for around £80 and you can add a different glass of good wine (chosen to compliment the dish) for each course for an extra £70. Highly recommended.
p.s. this restaurant is similar kind of prices to Coq d'Argent