Not a big difference. From Преображенская It would be easier to get to Sokolniki park which is one of the best parks in Moscow (I live in Sokolniki, I know what I'm talking about! ) But Elektrozavodskaya isn't too far away also.

If you're going to study in RGGU you should defintely choose Novokuznetskaya, because it would take you like 25 min to get to the unversity. How far is the flat from metro? It's better be <15 min. walking.

And you can definitely get from Elektrozavodskaya to the Red Square by walking, it would take you just 1.5 hours