Your Advice

Summon your waifu/husbando. FGO is waifu oriented game, not gameplay.l

https://grandorder.wiki/Upcoming_Summoning_Campaigns_(for_EN_reference)
predicted upcoming banners roll for love, you don't need to get all OP servants this game is way too easy for that.

You should just roll for your waifus. The game and almost every event can be cleared by even the lowest star servants, so don't hesitate to summon for your favorite servants.

https://grandorder.wiki/Upcoming_Summoning_Campaigns_(for_EN_reference)

Here's the upcoming banners for reference.

Many of the "must have" servants in most tier lists (this very site included) debuted last year so there isn't much in comparison to save for but if you want someone who'll be a huge boon for you then I would suggest saving for the scummiest of scummy mages who hasn't received a solo after the one he gets later this year since.

AKA Merlin

Read the upcoming servants list and decide this :

If you want waifu/husbandos then it's up to you, because favorite servants > gameplay.
If you need gameplay, Caster or support is the strongest class and the most powerful unit in this game, other than that just focus to cover ST AOE and other holes in your chaldea.
Caster big names : Waver ( no comment ) and Merlin ( no comment ) and for more than a years later it's Skadi ( no comment ).

Go for waifu but you should pay attention to the Alter-egos in SE.RA.PH event, and Ereshkigal and Abby at the end of the year (?.