Emiya

If you don't have a 5* AOE archer keep him for sure... he is a solid servant.

He is a good servant. Was my tutorial 4* and carried me through so much early content.

Though guda guda rerun is next spring for a np5 AoE archer if you prefer

He's one of the best SR archers along Kuro. With his two rank up quest he becomes a crit monster, specially with his second skill which gives him 50% crit at lv 1.
He's worth leveling,

Emiya is a weird one. His AoE Damage isn't that high, his NP5 damage is comparable to the NP1 of a lot of AoE 5* Archers (but the comparison dies when the bonus damage applies).

The thing that sets Emiya apart is that he can do the Raikou/Lancelot stuff of using his NP to clear wave and then use the crit stars generated to crit extremely hard (100% crit up). Of course, he's no match for Gilgamesh or Tesla who can deal ST damage with their actual AoE NP, but he's definitely a strong choice...I would say he's like Saberlot (his NP deals low damage but he packs the crits), he's awesome for a 4* but falls short when compared to most of the 5* choices like Nero Bride or Okita...unlike Munemori, who has something to offer even when compared to those two.

If you want to use him. Clear his interludes, his strengthening quests and level Hawkeye to 10 ASAP. Without those rank up quests and high-leveled Hawkeye, he will not have his sick stargen and 100% crit up...those two are the only reasons he's good, without that he's just another pre-buff Siegfried with nothing special.

Plus, he's cool af.

You can use him as a boss killer and as a daily farmer, he can crit real hard and he can survive longer if you put him on a harder content. He is a complete package of Balanced Unit.
Def up + Atk down + Evade for survivability ? That's very good and with a little or some help he can even tank some Bosses NP.
Crit damage up + 100 % + Card effectiveness up + Crit star gen up ? Lol, that is really nice.

Emiya truly worth the Investment.

They are different things.

One is AOE Buster NP with David/Arjuna/Cu Caster deck, who cast AOE attack down, is flunky in his skills untill ST Quests (2 of them) fix him into a stargen/crit machine. Also, is good to farm saber nodes.

The other is a ST Arts, and a spammer of it, can +50% her NP bar, can Arts Brave Chain with her NP, and crit even harder with Mind Eye Fake. Also, has Projection. A natural-born boss killer (specially those pesky midboss Spriggans).

Do level Emiya if you have no Gilgamesh/Tesla/Ishtar/NP5 Nobu.
But you will have to invest a lot (4th ascension to unlock those Strenghtening Quests) to make him worthy. Also, do the 2nd interlewd, to make his NP base dmg be not as bad as it is...Projection lv 10 will kinda fix that, tho...

i have both of them as well and i have leveled up both.
i would say he is worth rising for many reason.
1- personally, i like servant whit aoe st flexibility like him. some servant can only do 1, but him can do both. you use your np for weave and his crit for the boss (and boy he crit hard, i did 190k damage whit 1 art crit when i paired him whit hans and weaver). this is personal preference tho ( i also use lalter and cleo in the same way)
2- he is different. he is an aoe servant whit arts crit. kuro is an st spammer monster. she can crit ( and her kissing freak skill at level 10 give tons of crit star) but she is not a "true " crit servant. her crit buff is tied whit her evade, and i dont like it.
3- nero fest. man i wish i had a good emiya back then. defence ignoring np would have be so good.
4-make the emiya family team. kuro, emiya, emiya assassin, iriesvild and illya.