What would ROTS Sidious think about these historic figures if he met them?

As another question, if Dooku wasn't in the picture (let's say he saw TLJ and TROS and had a heart attack), would he try to recruit any of them as his apprentice?

Emperor's Wrath (act 3).
Exar Kun.
Vitiate.
Valkorion.
Arcann.
Vaylin.
Nihilus.
The Outlander. 
Karness Muur.
Tenebrous.
SoR Revan.
Darth Nox (act 3). 
Darth Malgus.
Cade Skywalker.
Darth Caedus/Jacen Solo.
Anakin Solo.

He would recruit as an apprentice anyone with potential rivalling his own who is also susceptible to being manipulated or dominated. This would include Vaylin, Cade, Anakin and maybe others.

Those who are too weak to ever surpass him he may try to recruit as an underling, or if they are Sith they would be destroyed as they breach the Rule of Two.

He would see Vitiate/Valkorion as a rival.

I think he would view them through a pragmatic lens primarily. But I'm guessing this thread is asking for more what he thought of them as individuals.

He would view Tenebrous as a short sighted fool. Nihilus as nothing more than a Force sinkhole. Darth Malgus as a pioneer and adherent to his own philosophy. I'm sure he would regard the Eternal Family with contempt because they share power and do not devote themselves to the dark side fully - whether that be because they try to incorporate other aspects of the Force or because they have a glint of the "impotent side of the Force" tucked away (Arcann). I'm not really sure what he would make of Revan but I'm not sure it would be pure contempt. Caedus would be seen as a Sith pretender. He would think of the likes of Cade or Anakin Solo in purely pragmatic terms. The Outlander as just a contemptible off-shoot of the Jedi. And the remaining Sith as powerful enough in their own right, but ultimately anachronistic and unworthy of carrying on the Sith mantle.

Hmm, interesting. You don't think he'd try to recruit the Outlander?

I don't think he would get very far.

Lol true.

Most of individuals on the list Sidious would see either a threat or a rival. Darth Sidious would definitely would seek Cade Skywalker, because of Dark Transfer ability.