I got cards from both Megafon and MTS and have been using them for 4-5 days, first in the northern outskirts of Moscow, and then in the Vladimir, Yaroslavl, and Vologda regions.
Technically, MTS is definitely ahead. Sometimes works even in 2G areas while Megafon does not. This post was uploaded via 2G Internet somewhere in the Vologda region.
The MTS card was easy and straight-forward to buy.
Buying the Megafon card, on the other hand, and getting some use out of it was close to an ordeal. The pattern was very similar to last year’s. The card failed, the payment got cancelled, technical support was hard to reach and could not help anyway but instead was sending me to the accounting department that could not say anything beyond “our system says your balance is negative”. Dealing with Megafon was time consuming and highly frustrating both in July 2012 and just now, in June 2013. If you run into problems on the road, you won’t find their offices where they are supposed to be, and when you find one you may discover they are not connected and will not fix each other’s mistakes. In Kandalaksha last summer I was explicitly told bythe local Megafon people that buying a card in Torzhok, as was the case, was not a clever thing to do, and a grown man with a beard should have known better.
In Kandalaksha however their service is reliable, and Alexandra, who’s been using it for years, has nothing but praise for them. But she never tried Internet while on the road.