The terms "Russian mail order brides" and "Russian mail order wives", widely used by Americans, can be quite misleading as it almost creates the impression that the ladies would agree to marry just about anybody, which is miles far from the truth.
Both Bulgarian ladies and Russian brides are amazingly beautiful women but you will find that a greater percentage of Russian girls will have professional or better quality photos.
Bulgarian ladies have free access to Europe without a visa and can on the one hand easily find employment outside Bulgaria and on the other hand visit you without fiancée visa complications if you intend to take your relationship to the next level.
Once you have met with your Bulgarian bride or perhaps Russian bride and you find out that you cannot live without each other you will consider taking her home with you.
For the Bulgarian ladies this is much easier as they can move unrestricted around Europe and more and more visit visas for the USA are being granted to Bulgarians (we have heard that some 50% of the people who apply do get them).
The Russian Mafia runs the cities and bribery and corruption are abundant.
Airline tickets are also more expensive because of the greater distance to travel for meeting the Russian lady of your choice.