It is better to go direct at Qatar Airways. Yes thebigticket is correct, the earlier the better since when date is nearer the Airline ticket price will be higher as compared when you book on the earlier date. But just be sure on the dates since if the ticket is issued and you want to change it for any reason, you will pay a penalty of Qr 500.00 as a minimum.

Seasonal dates also is a factor. Mostly Airlines charge higher fares on peak season than on low season for obvious reason.

Agencies such as Regency, World Travel, Al Deera, Cleopatra, etc.. are good choices.