4 Star worth of Grail

IMHO, both Chloe and Saberlot are pretty strong contenders. And having watched Herc solo (except for the 1st round) Goetia, if you get him to bond 10.... even I'd have to consider it :)

Herc - yeah we know why.

Chloe maybe, since Orion is... lackluster and can't spam a NP5 like her.

Saberlot is one of the few exceptional 4* that could outperform the 5* counter part servant in his role (Nero Bride as Arts ST Saber - at least before her strengthening). Grailing him will definitely take his usage potential to the next level, but then this year we will get yagyu which might be even more OP.

Arash is another exception imo, not just because of his AOE damage, but also his self-destruct/free immediate member change. And graling him up is cheap for the first few extra levels.

I personally prefer to grail 5* because I only want to focus on servants that are absolutely best in their roles, or servants that I like most. Those above are the exceptions.

Besides of Waifu/Hunbando reason, grailing SR are mainly focusing on purpose for maximizing their damage, particularly if they have decent skills, or NP5 ST (walfare servants). Therefore, I can see lots of people grail Kuro, Lancerlot, Artoria Lancer Alter, Kintoki since their potential damage in Lv90 can be fairly comparable with SSR.

It also depending on your SSR servants in same class, as well as you team building thought.
For instance, if you have Merlin, Waver, but dont have strong SSR ST saber and Altera, then grailing Rama even worked.

Same thing, some people grail Lancelot generally because of the fact that 3 ST SSR sabers thus far (Okita, Musashi and Umu bride) are limited. Grailing Shiki because besides of Jack, all other SSR assassins are also limited.

Grailing Herc, is....Because of his damage can be pair-able with his durability in this case. Bond CE Herc will be always top-class as SR. Berserkers are famous for their high versatility against any class enemy, particularly worked as mob-cleaning. But many Berserkers are glass cannon anyway.

Hello.

Chloe is amazing, NP5+Halloween Princess or Holy Night Supper MLB is a tactical nuke, one of the best archer in the game, and with a little low HP for a 4*, do recomend.
Saberlot is the best 4* saber, his crits overwhelm class disavantage and sometimes even his NP, sadly he has no survivability, so grail is also good
Emiya (archer), meh, I dont know, he is fine in level 80. Hawkeye crits are really OP, you dont need much more.
Lancer Alter Arturia absolutely, she in grailed to 90 surpass OG Lartoria in raw stats, and with 2 skills better than hers (just inferior in charisma), so literally better than a certain 5*s.
Hercules, if you bond 10 him, yes. If not, save grails for this time.

Depends on what SSRs you have in your roster. All the listed Servants are decent Grail candidates if you don't have--and don't plan to roll for--a stronger Servant of that class with the same type of NP (ST vs AoE).

For that reason, I'm going to go against the crowd and suggest not Grailing Herc. Level 100 Cu Alter will perform better in almost every scenario. Cu Alter is just as survivable (without needing Bond CE to do it), in addition to having better team utility with his AoE Attack/Crit down. Herc is more selfish and his damage will suffer long-term since you won't be equipping a damage CE on him.