235,000 stardust, who gets it?

mewtwo by far

Both of these options may seem good, but both do require a lot of analyzing.

Not sure how effective a ganger would be against giratina, SC gengar does output a lot of damage, but Giratina has high bulk, and likely will get shadow claw itself. As for mewtwo and the others, Tyranitar seems like it'll be a better option, but if you are purely concerned about damage, ganger will work (but DPS drop form whipping out/fainting may need to be considered before final decision)

Articuno may not be viable, Dialga and palkia are not weak to ice (with dialga being part steel so articuno's weak to it) leaving only giratina, who's best counter will likely be Tyranitar. Against Rayquaza it may be an option, but whether Rayquaza returns before gen IV remains to be seen, so I would hold off on it until we get confirmation of either Rayquaza comes back or Gen IV launches first, as theres 3 ice types that can take the spot of Quaza killer (and even then, i'd wait until the day of to power up so I dont get screwed last minute) as well as Smack down tyranitar is a thing, so unless you dont have many with smack down or tyranitar candy are scarce, or, dont have any good poliswine/sneasel/eevee or their candy, that can evolve into the gen IV eveolutions, articuno would be good, but I do advise waiting

Sorry If I talked in circles about tyranitar, but it does seem like it will be the best option for gen IV

Shadow Claw Gengar. Rayquaza is very unlikely to return and Ghost would be slightly more useful in the future.

Neither. Save your stardust.

If you're really just worried about Rayquaza, double ice Jynx is a good option now, but Mamoswine will probably be a better option later. And it doesn't require rare candy, unlike Articuno.

Or just power up your own dragons - sure, they are weak to dragon, but a random raid boss Rayquaza has Air Slash half the time, and two thirds of the time has either Ancient Power or Air Attack, while your dragon will have Dragon Tail/Outrage (or Draco Meteor or Dragon Claw) 100% of the time, since you're not picking attacks randomly. Rayquaza on Rayquaza is a really good matchup - worst case the boss has dragon moves, and your Rayquaza is a high DPS glass cannon, which isn't a terrible thing in a raid.

You are talking about investing now for using them in the future. Mewtwo, at least is here and you can use gengar next time you get an EX invite.

I did max out my shadow claw gengar (14att) and use it currently for Mewtwo, kirlia, alolan raichou, machamp solo... It's fun, but glassy.

I did power up to 35 articuno and used it against rayquaza. It was also fun, but we don't know when Ray is coming back.

Now more than ever, the sensible advise is "save your stardust".
Shadow claw gengar might come back from research tasks and you'd regret getting a better one.
By the time Ray comes back, Mamswine might be here and be a better option than articuno.

In conclusion. If stardust is not an issue and you want to have fun now, go ahead. I recommend gengar as a more versatile and fun pokemon.

I vote for the Articuno.

The 100% Artic all day long! Never gonna beat a 100%er

Gengar doesn't cost any rare candies so I would definitely power it up unless you are low on dust.

Hold on articuno.

If you are not planing to use it now, keep your stardust, we dont really now what will happen in the future meta.
If you gonna use it now, i choose Gengar Shadow Claw. Very good against PC Mewtwo, and still usefull against the Confusion one.
It is maybe a good counter against A.Marowak withouth depending on the weather, need to test it though as my only one A.Marowak is dex opening so i raid with many trainers
As for A.Raichu and Kirlia definitely very2 good.
But i like using glass canon, some trainers dont like it. If you never use one, better try it first against Kirlia No need to power it up yet and see if you like it or not.

Articuno takes rare candy, and is very likely going to be outclassed by Mamoswine when 4th gen hits.

Gengar, on the other hand, will still beat Giratina in DPS once it arrives. Chandelure in Gen 5 has an attack stat slightly higher than Gengar, but does not get access to Shadow Claw.

I'd say the Gengar is more likely to remain relevant for a longer amount of time.