My room is 25 sqm too and i am using 5.3 channels. My take is quality, quantity can be added later if funds permit.
IMO, 2 or 2.1 is better for audio, 5.1 up is also good for audio and best for movies. Everybody knows the movie Starwars Phantom Menace Podrace scene and Book of Eli small house assault scene...this is a very good example showcasing surround spkr.
Not all movies requires a surround spkr, but its best you have this so that you will not miss the fun of surround channels when it is needed. Enveloping 3D sound experience really gives a thrill which 2.1 will not offer you.