They are interchangeable and they are not, all depends on the circuit.
Strangely enough many ECC88 sound better with more air and musicality compared to their bigger cousins like E88CC and E188CC. Unfortunately they do not last as long but still that depends on the circuit.
Throughout the years i have liked many tubes, all different, even the ones made with same tooling (Dutch, American, UK, French, Indian). French tubes for instance have the same nice mids of the Dutch tubes but with nore sparkle at the top end.
Always preferred the early Siemens to Teles and good value were the early Teslas and Tungsrams. Another excellent and underated tube is Raytheon 7308.
Anyway my top favourites are 6n23p Voskhods 74-79 period, followed by (not in particular order) early Cca’s, Amperex Bugle Boys ECC88 straight D- getter, Philips Miniwatt SQ early 60’s or E188CC PQ same period, Telefunken PCC88, Mullard E88CC-01 (CV2493), RT or Dario E188CC, Siemens E188CC A frames, Amperex ECC88 orange small o getter, Amperex USA PQ whites.
Great period for all western tubes (with exceptions) 1962-1965.
Most of them are good for phono stages and line stages but please remember that unless they are rugged like the russian tube all can become microphonic due to their construction. Line stages with high gain are not a very wise mating. A tube being noisy on a line stage can be quiet in a phono stage.