Talos or cronos

I need a bit of something big maybe just to draw the big guns off my warriors or hopefully deal some damage to my foes, which is in general the best choice and in what kind of numbers is a haemonculus neccasary?

It depends what you need.

If you need a fire magnet the talos, if it's to buff your army, chronos.

If you can, field formations from the coven dex, dark artisan is good, CtC if you have the points.

Build towards a Dark Artisan. Very tanky and a bit of a bullet magnet until your opponent learns not to waste shots on it aside from heavy weapons or grav. Fair offensive capabilities even if the unit is a bit slow. They do have the option to deep strike if you take a webway portal.

Choosing between the Talos and Cronos solo. Talos first. The spirit probe on the Cronos is nice but, its range is only 6 inches and DE are fast and don't tend to castle up.

Are any of them worth the points?

It depends against who. They are fery durable against some armies and stupidly fragile against others. Thing is most meta armies fall into that second category, so theyre not in a good spot right now.

Most common army in the game is Marines. Most common special weapon type for marines to carry is grav. This combo hard counters the lot. It's not that we're tailored against, it's that we're explicitly weak to what is most common. That plus a lack of compensatory free rules are what hold us back.

corpse thief claw 600pts can generate its pts back easily.
I have run it as well as dark artisan and gone for bufs with cronus.

the free 6" scout move and the points it generates makes it lovely

Solo Talos is a solid take. Even if killed - he probably make his point back.
Cronos is harder, much harder to just insert into any army.