Archuria or Chloe

Chloe is more selfish, and her NP does more damage (about 10k more). Also, she can get her NP off faster every few turns since she has a quick charge skill, but has slightly more trouble spamming it.

Archuria has stronger team support (party-wide attack/defence up, NP drains enemy NP) and spams her NP more easily. NP does less damage. She also does much more damage on her normal attacks.

Up to you which you think would benefit you most, personally I would go with Archuria.

Archuria will be more useful when you are new. Grab a support Tamamo and bring Hans with you and you have a team that can take most content while you level up other servants.

Level both of them, slap Tamamo as their support and throw Medea, Kiritsugu/Assassin Ryougi and Waver in the back line and you have an unstoppable arts nuker team. This is what I'm trying to build at the moment.

Archuria is the better servant. But level Chloe first. Chloe requires far fewer mats and can be max ascended quite easily. Eventually archuria (once you get all 30 of those knight medals) should replace her but at least initially Chloe would be easier.

Normally every SSR are recommended for leveling first. Especially for Archuria as a top archer, only Orion, Gil and Rin could be comparable but they worked in different way.
Off course Kuro is also one top SR with amazing animation. She also worth for lv90.

It is really hard to choose. Archuria is in fact worked much better in NP2. She can even solo some sabers with limited NP damage (or maybe AOE NP like Gavin).
If you want to build a art critical team like using support of Tamamo + Waver (Hans), then Kuro is better. If you want to build a NP spam team, Archuria should be more focused. Personally speaking, Archuria NP2 >> Kuro, But Archuria NP1 depends on what playstyle you want.