I'm not a fan of SU premium eco. Yes, you get more food than in economy. Yes, there's more space than in the average economy seat – but that's it.
On the other hand, the seat doesn't recline but slides forward. This strongly reduces actual leg room. You also can't comfortably turn in your seat. On my last flight booked in A, I voluntarily downgraded myself back to eco (row 17) in order to get my legs up.
Also, Aeroflot is inconsistent with their miles. Last year they sold A as a premium fare (200% miles), however I only was credited 150% on the actual miles flown. Only 1 announcement in Russian had been made on their news site.
If I had the choice between Aeroflot 77W Eco and Comfort (premium eco), I'd go for Eco, then select row 17 (all) or 18 (seats C or H) => Expedia allows you to see seating availability BEFORE booking the flight. Aeroflot's "value" fare class (M, U, K, H, L) also gets you 150% miles.