I currently own a Heracles and a Li Shuwen as my only 4* Servants. I was thinking about going for EMIYA, because I like him and he seems to be quite okay later through his strengthening quest. I was also thinking about going for NP2 Heracles, or are there better servants to choose from that list?
Out of everyone on that list, Heracles is the best choice, hands down. But since you're light on 4*, there are tons of options that you'll feel good about.
I'd aim for Emiya, Carmilla, or d'Eon. They're the better choices in their classes from that list, and you've already got Herc and a better Lancer.
NP2 Heracles isn't that worth it since the defining trait of Herc isn't his damage, but his survivability with his lvl 10 bond CE. But he is a really good servant and stays relevant in the future so further improving him might be a good choice if you don't have any preference.
EMIYA will be a good servant in the future but for now he's a pretty average archer.
Tamamo Cat is great for farming and can help save a lot of time, but she's only good with a starting NP CE, as per the usual with farming servants.
Carmilla fulfills a rare niche that is as a niche female killer. She can also spam her NP relatively quickly and can generate stars for the team. Outside of that, she's a decent servant.
Marie is an excellent staller thanks to her 2nd skill giving her a 3-hit invulnerability and heal.
Chevalier can be a tank if you need one, but Mash can fulfil that role if not better.
Martha is a pretty average support that can heal and cure party debuffs, but other servants can fulfil that role and some are arguably better than her (Hans and Medea once her strengthening quest is released).
Siegfried has the stats of a tank but unfortunately doesn't have the skillset to fully maximise that role. His damage is low and his only niche is killing dragons, which he can't really do that well because of his low damage and reliance on NP and buffs.
Elisabeth is a decent support primarily focused on dealing more damage. However, other supports do that better and more consistently and she doesn't have any redeeming qualities aside from that. Her damage is low and although her NP can help with farming, she need further support and CE help to do that as well.
Stheno can only charm lock males and does nothing else outside of that.
We just added in a new article that gives some more context/advice on picking your free 4 star! Since you already have Heracles, and you only have two 4* servants, I'd probably recommend diversifying your servant pool. At the end of the day, choose who you like best!
