my money is on US and/or UK. they seized the moment of chaos and destroyed the pipeline permanently. they have a lot to gain from this. it simply weakens EU, makes it more dependent on US/UK, weakens economy, etc. UK is not EU's friend and US is only a friend as long as EU falls in line and you never know in the future.
Russia could have done it too but it makes no sense and most importantly they have a track record of failing and getting caught with even simpler schemes (e.g. novichok attack).
just the fact that US is not jumping to blame Russia this time and Sweden already said they treat it not as an attack on Sweden (so if it turns out US did it, Sweden is just gonna say it's in international waters, not a Swedish asset, etc.). I mean US intelligence knows what Putin has for dinner. Impossible they don't know who did this, in NATO waters. Only EU doesn't know. US/UK surely know and if it was Russia they'd publish video footage 1 min after explosion.