never strider unless in an all hero force at 350pts imo

How come? 350 I have decided on Boromir of Gondor with either a Captain or Faramir. But for 500 and 600pts, Boromir COTW, Strider, Elessar?

Aragorn just costs too many points and brings down your model count. So most missions become increasingly difficult.
For 500+ Aragorn can be very useful indeed.

The only way I see aragorn in 350pts is if your partner goes
E.g.
Halbarad
Loads of rangers n RON
or
Twins
Loads of rangers n RON
or
some cheapish leader
shed loads of troops

Boromir of Gondor. Him, you can actually back up with a decent amount of regular guys, so if he gets transfixed, no big deal. If there is something that can actually go toe to toe with him, then it can take on Aragorn and Boromir CotWT as well, except then you will have less regular models to deal with the issue.

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"...in the end the Shadow was only a small and passing thing: there was light and high beauty for ever beyond its reach.”

Completely disagree.
2x 0 7 0 ring wraiths will remove boromir from the game for around 6 turns with no trouble where as boromir CootWT can ignore a couple of transfixs and when he needs it use will to run rampant.

I figured Wraiths would be he problem. At 500 and 600 Boromir COWT or Strider or Elessar?

Depends largely on what you are fielding- I tend to go in favor of theme when I can, and imo, they both are adequately effective for what they do.

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"...in the end the Shadow was only a small and passing thing: there was light and high beauty for ever beyond its reach.”

I recently watched a game where the Boromir of Gondor lost 2 wounds to Goblin archers the other day, and there was only 3 archers that aimed at him.

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"I am the Flying Spagetti Monster. Thou shall have no other monsters before me"
-FSM.

Ouch. Ouch. Ouch. Poor Boromir. That, imo, is why one brings the elven cloak- if one can.

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"...in the end the Shadow was only a small and passing thing: there was light and high beauty for ever beyond its reach.”