I will carry EURO with me.
How is the airport? I guess it is bad price?
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Obviously all exchange offices in the world charge some explicit or implicit commission. In Russia, almost always there is just implicit comission in a form that the exchange rate at the office differs from current market exchange rate at Moscow Interbank Exchange. So each exchange office has exchange rates clearly displayed and that's excatly how much rubles you get per one euro, no additional commission is taken. The only difference between exchange offices is this rate.
Nowadays that the market exchange rate can change substantionally within one day, all exchange offices change their exchange rate several times per day, and many online services may have outdated information. So the best option is to know current market exchange rate and look for offices that offer a rate close to the market rate. A difference below 1 ruble is very good, and below 2 rubles is still bearable.
However, you might not be able to know current market exchange rate. In this case a good criteria is the difference between buy and sell rate at a particular exchange office. (Obviously, the market rate is something in between.) So, a difference between sell and buy below 1.5 rubles is a very good deal, below 2.5 rubles is quite good, and above 4 rubles is quite bad, usually it is easy to find something better.
However, you should also consider the tradeoff for money versus your time. The difference between the best rate you can get and the rate you get in the nearest office will usually be below 4 rubles per euro (and often even less). If you want to exchange, say, €200, the difference will be 800 rubles, which is about €11. It is up to you to decide whether time spent looking for a better price is worth this profit.
It also should be noted that in many places in Russia you can pay by a credit card (Visa/MasterCard/Maestro), so you might find that you do not need cash that much. (Do not hope to cope with credit card only, but you might expect up to some 80% of all spending to be done by credit card.) Check with your bank what exchange rate and comission they will apply for credit card ruble transaction and for withdrawing rubles from ATM — you may find some option chaper than cash exchange.
The airport exchange rate is usually not very good; there are, however, a lot of exchanges in Moscow proper, and will have signs outside their offices listing the current exchange rate, but be aware that many of them won't speak any language other than Russian. You'd probably have more luck finding someone who speaks English/other languages at one of the national banks, but the exchange rate won't be as competitive, and you might have to wait a while.
Also, be aware that money exchange places in Moscow tend to be very, very picky in terms of what bills they're willing to accept; I'm usually coming from the US, and they will only accept $20 bills, and those bills have to be immaculate. No writing, no tears, no ink stains, and no creases/wrinkles. I'm not sure if they're quite as picky at the national bank branches. I go through the money I'm going to bring to Moscow before I leave, and I usually end up having to exchange 2/3s of the bills I get from a typical ATM for other bills.
Most bureaux de change around the world advertise their commission as 0% and make profit through the difference between the advertised exchange rate and whatever is the Central Bank's exchange rate on that day.
Your best bet is to use a website to compare all of the exchange spots in Moscow and find the one with the best exchange rate.