Well lets see,
"I don't think there are any ships with such luxus cabin
as on Epic (in Economy Class of course)."
From personal experience I would suggest Disney and the ships of Celebrity. My balcony on the Disney Magic was outstanding and my basic inside on the Celebrity Century was nicer in many ways to my balcony on RCCL Adventure of the Seas.
Based on my experience in the main/premium market, I would say again the Disney Ships & full Celebrity fleet would out shine the Epic, as well as perhaps the other ships in the NCL fleet.
It's odd as I write this; but in many ways I think my very best cabin was, the basic grade inside I had on the Century. It had dark red cloth walls against the bed, a raised sink in the large bathroom, (with many large bath products included) three large closets, with a full chest of doors, two bathrobes, a nice small table with chair, a full wood based accents on walls etc. The room service was outstanding (including New York Steaks etc.) and the service was very fast.
I should also mention that the ship had one of the best dinning experiences I have had in my life; the Murano, which had tableside preparation & presentation. Even the one gala brunch was something to remember. It is impressive when one considers that the Century is among the oldest ship in the fleet.