Best 3 star Archer

Robin for ultra nuke and Euryale for anti-male nuke. You really need them both and they are not expensive to max.

As stated Robin and Euryale are the better of them Euryale is generally considered better than Robin in spite of being more niche as an anti-male servant.

Team utility? David >=Kid Gil > others as 3 star archers

All 3 star archers has their own superiority and weakness. There is no "best"

Mr.Green is capable for shooting amazing NP. But it is hard for him to accumulate another NP shooting. So far he is capable for one shot Sabers and Berserkers but later on it is hard, like boss fight in JP. His skills are also good for short time bursting damage rather than long-tough challenge quest. Hence, many SSR/SR Archer can work better then Robin wont be so shinning in the future.

Gil is good to take him into team. Just dont quite rely on his charm skill since it is high cool-down and not 100% successful (I prefer Stun). And besides of his NP, he still cannot provide any hard-defense buff to the team.

Euryale is theologically one best 3 star since she has great niche versus any Male servants. In this case, she even works better than Orion. But when not fighting against Males, she wont provide any help. Meanwhile, team composition for her is also not flexible, normally with Sisters to accumulate effect against Males, or with Tamamo for better NP gain and damage. It is good to grail her because no matter when, Male enemies will always existed no matter what class, even a Male lancer Sisters can still do something effective.

You dont ask David but in fact David has golden-ranked 2nd skill which make him good for team. His 3rd skill is also an supportive skill and 1st skill can help him stand longer as 3 star. He can only be replace by Tristan theologically, but 3 Art card make him also very compatible for a supportive role.

Robin Hood and Euryale are both nukers. Euryale dominates male sabers and berserkers where Robin Hood is good against anything that isn't a lancer.

Kid Gil is a bit different. He's pretty much just a 3-star version of regular Gilgamesh. As opposed to the other two, Kid Gil has an AoE NP and is a more buster-focused archer, as opposed to arts-focused. He can help clear waves of saber minions and then inflicts NP strength down on bosses. So while he's not the boss-killer that Robin Hood and Euryale are, he has good strengths that shouldn't be ignored.

All in all, there is no best. All the 3-star archers are good because they each offer something unique to a master.

IMO
Euryale > Robin
Arash (1*) > Kid Gil

Arash has a stronger NP and can charge it faster, he is therefore more useful for farming than Kid Gil. If you want to kill bosses, go with Euryale or Robin. Both are fine, but I really like Euryale because she can charge her NP very fast, she can use a charm, and her NP is killer against males. Robin's NP is insane but its damage highly relies on his poison skill. That means the second NP must be fired within 5 (?) rounds, which is pretty hard to pull off. Otherwise the damage is quite miniscule in comparison.