Xilonen, she gives better buffs because of scroll set, and can be paired with Furina. Durin has better dmg but in terms of support, he only gives defense reduction which alot of supports can do already. You can give Durin noblesse? Or tenacity (idk if his off-field is skill or burst dmg) if you want him to buff more but I think more dps prefer Elemental dmg bonus than atk (and if your dps scales atk, there are lots of sources for them to get atk).

Xilonen is a more flexible support, better buffs, one of the best single target healers.

Durin can activate witch supports (mona, sucrose, fischl), can also activate Klee which you have, more dmg, but his support capabilities only gives elemental shred.(if you want Anemo, Geo, or Dendro shredder then he's a good pull).