he's not just a dragon. he's the best dragon.

I don't side with the Blades or the Greybeards 100%. I side with Paarthunax. The Blades treat me like crap. Delphine goes on and on about how the Blades are supposed to serve the Dragonborn, but, apparently, serve means boss around while she does absolutely nothing. The Greybards piss me off too. They know all these shouts and could give you the power to, probably, lay waste to the entire world, but rather than helping you do this so you can stop Alduin they sit around in a temple and MIGHT tell you which horror infested tomb you need to plunder to find a fragment of a Shout.

Paarthunax on the other hand, talks to you, helps you, tells you how to find the Dragonrend shout and meditating with him makes your shouts even more powerful. Is Paarthunax really worth killing? Heh, why isn't he worth keeping alive?

the fact that Dragonborn can kill him and absorb his soul making him just a dragon

Dragonborn job is to kill dragons, because they are threat to the world, we cannot leave one just because he claim he's become peaceful, he can change his mind later, who know? There is no guarantee he will remain as he is. He's there because of waiting for Alduin and the last Dragonborn. When Alduin is gone, and Dragonborn is dead, who know what he will do...maybe he become bored and going rampage, who can stop him then?

if he was to go on a 'rampage' he would most likely be kiled. his soul wont get absorbed but he will be dead. when Alduin returns again he wont raise Paarthy because Paarthy is a traitor to the dragons.
Braith would probably kill him.

That is a matter of argument and though I see your point I disagree.

The job of the dragonborn is to kill Alduin according to the prophecy, it says nothing about slaying every dragon on Nirn.

Our job is to keep Alduin from ending the kalpa prematurely. It is the viewpoint of the Blades that we are the ultimate dragonslayer as we are the only ones who can keep Alduin from raising the dragons again. With Alduin gone this is no longer necessary as once a dragon is slain it will remain dead until the kalpa is ended. Should Alduin return in his world eater form and raise the remaining dragons before ending the kalpa there will be no one who can stop him and the world will be doomed anyway. And there is no evidence another dragon will be able to raise the dragons making this point moot.

With Alduin gone anyone can slay a dragon and without Alduin its demise is final, at least until the point I mentioned.

If you don't kill him, he have his army of dragons, he will become their leader. If he killed anyway, there are dragons out there that can assume command, when Alduin return, Alduin no need to rise any dragons, because there are already dragons, the world is doomed...it is because the last Dragonborn didn't do the job to cleanse the world from dragons.

Alduin will return it is a sure, but if return alone, there is no much threat and sure the divines have their own plans, either Alduin will doing his job to destroy the world, or someone can stop him, or Alduin is dead somehow when he return, we will never know and it is not the last Dragonborn concern, it will happen maybe hundred years later

But, if the last Dragonborn do not kill Paarthunax, the world will sure destroyed when Alduin return...

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If Alduin returns the point is moot as the kalpa will be ended. The LDB need not destroy every dragon as anyone now can do so, army or not. As I said in an earlier post my DoVahkiins feel more affinity for the dragons, at least for three of them than he does humanity or mer. Every player has this decision to make.

Any dragon that attacks me will die, those that do not do so unless they are the subject of a word wall quest will live. That is my way, your way is yours. there is no right or wrong answer and everyone should do as they please in their game.

Have fun with tracking down every dragon in all corners of the world, especially since the game will continue to spawn them inifinitely till you walk away.

Depends on the play through. Alduin killed him once when I used Storm Call; it got him weak enough to get offed by the World Eater. I killed him once on a power hungry character. Ebony Blade and Blades Armor go hand in hand. I usually roll with the Greybeards. They help find WoP and Paarthurnax is the only source of decent lore coming out of Skyrim, so there's that. Siding with the Blades gives you unlimited Dragon Souls early on though (after they finally patched it) so it's actually a viable option and you're not being a jerk for the lulz. Delphine is condescending, but whatever.

Just like how the world was surely destroyed when Hakon and company didn't kill Paarth in the past before we showed up.

Here's the way I see it: Neither option is good at what they do, while Parthuunax is caught in the middle, just like this discussion.

The Greybeards remind me of the BoS of Fallout: Keep technology, but don't use it except for self interest. The Blades are defunct, "lead" by someone who has no guidance, has never had guidance, and can only bark orders because "OMG! I'm needed!" and freaks the hell out.

Both should have respected the Dragonborn, but neither side did. Instead, the DB has to do everything themselves, which leads them to Parthuunax.

Now, we're at a situation. Here's a dragon who helps us, right down to giving us the very power we need to defeat every dragon, and yet, does so knowing our sole purpose is to kill them.

I don't know about you, but a dragon who goes out of its way to put this kind of power in the hands of an "enemy" deserves to live.

I think the people who spare Paarthurnax fall into two camps:

1) The Blades have fallen low since the previous games and their demands are illogical and cruel, so I'll spare Paarth.

2) The Blades aren't worshiping the very air I breathe, so I'll spare Paarth.

You forgot the option I mentioned: 3) The Dragons treat me with respect so I side with those who befriend or follow me.

Yes, it is worth it. Plus you get Esbern's potion

4) Paarth has been tried by the people of Skyrim and found not guilty. The blades don't deserve to pass judgement. They weren't even on Tamriel when the dragon wars took place.

Oh my god. Not you again.

After what you said before on the topic I'm not sure you even know what the dragons are.

^^ And this. ^^

Which has never ever worked. I haven't even bothered with it since it was supposedly patched.

It works with 1.9 I tried it and then reloaded a save before killing paarthy.

I never killed Paarthurnax, and I do not plan on ever doing so. Delphine and Esbern can die in a fire for all I care.

It works now. Probably the biggest reason to join/stay with that faction. You can still get it before getting the Paarthurnax quest if you're interested. It's most valuable for characters that don't use shields.