All accounts have Skadi, but only 1 has Waver and none have Merlin and the blue cat.
1 account has a lot of good SSrs, one has a couple of good SSRs but none that work with Skadi (no Waver), and the last one has only Skadi+Amakusa+Caster of the Nightless City. So I can say with experience I’d rather have all 4 supports.
If I were choosing I’d rather have all 4 Infinity Stones and no other SSRs than multiple DPS SSRs and no Infinity Stones. The Infinity Stones can make every servant great but a lack of buffers really hampens your progress through the game both in terms of the number of turns farming will take as well as the degree to which boss fights and CQs become huge pains in the ass.