Why did Palpatine care about Anakin (Vader), especially when considering his powerful "future Force visions"? Palpatine organizes the framework-setting Order 66 to kill the Jedi. It is Palpatine who defeats Yoda.
It is Palpatine who pretty much organizes the whole thing. He organizes the Death Star, his ascension, the destruction of all opposition.
It is Vader who tells Mace about Palpatine being a Sith. It is Vader who gets sushi'd by Obi-Wan.
Vader is the only survivor of the Death Star Mk1, but he was never the commander, the engineer or the saviour of the darn thing. Vader also throws Palpatine off a balcony.
While Vader does manage to murder a bunch of kids... that doesn't really seem that difficult a skillset for Palpatine to find to warrant any of the effort in winning Vader over.
Palpatine seems pretty cognizant of the whole "Sith kill each other", he doesn't appear to even need another Sith, so what? Was Vader just a really really good conversationalist?
To be clear, I'm referring to the prequels - as in, why does Palpatine have interest in Anakin "back then" - not just saving him, but, well, trying to turn him at all?
With all of Palpatine's "future Force vision" powers, Vader doesn't seem to be useful in the future or at the present, although he does throw Palpatine off a ledge... I'm just assuming Palpatine didn't see that, and wasn't, like, really into extreme sports
This related (not a duplicate) question suggested deals with the Sith code of ethics, and the strong ignoring the weak, and effectively asks "why would one Sith help another, junior Sith". It is an interesting question, check it out.
This question asks why Palpatine bothered with Vader, given both Vader's uselessness to the overall story arc (aside from killing Palpatine) and Palpatine's ability to see the future. It also (implicitly) inquires why Palpatine, who is solely responsible for everything that happens in the prequels, even bothered with an apprentice at all.