You are asking only about airfare so here it goes. It depends. Are your travel plans domestic or international?
If your plans are domestic, you can usually get awesome deals online.
However, if your plans are international, you would want to buy from a consolidator. Consolidators rates cannot be beat for international airfare. You would have to call the administrative department of your carrier of choice to your destination (Russia) and ask them who their consolidators are for your specific destination (Moscow). Get in touch with the consolidator and you are on your way.