Which first ?

I'd start with the level 20. You won't need to spend the dust and candies on it to get it to a point where it's usable like you would need to for the 6.5 or the 9 (unless you're looking to use in pvp Great league, maybe?). The level 35 could be evolved and utilized if you don't have other high level rock attackers.

I wouldnt say that the level 9 isn't worth anything even though it's IVs are rather low. I will always choose to power up/max a lucky over a non lucky even if its IVs are worst simply because the stardust savings are just so significant. (And IVs aren't really that important)

If you're low on stardust, always choose the lucky.

id do the 6.5 cause lucky and good iv's

Only 45 candy and 40K stardust from 6.5 to 20; 20K for lucky. If you are considering powering up the level 20, it is not too much more for the 6.5 lucky.

Almost definitely the 6.5. 13 attack should let you hit most break points at max level, which will be cheaper to get to cos of Lucky!! High attack IVs are important and ESPECIALLY on something like a rampardos. Wouldn't want anything less than 15 normally but 13 is fine with Lucky :)

Luckies save stardust, but this is less relevant for rare species like Cranidos, where the limiting factor is candy.

Easily the Level 6.5 96%.