In regards to PVP rewards, if you have a good leader
(ie: you managed to get Barris/BountyHunter/HK47/Ima-gun-di/even a high star dooku).
I would suggest to go for IG-88 first.
IG-88 was not 'nerfed' as hard as people think. He is still arguably the game's highest damage dealer. Lacking only in the HP department. Even his speed is rather decent.
Darth Sidious on the other hand, was nerfed hard. He was the glorious champion before Global Launch. WAS fastest speed in game, one of the highest basic damage, best leader's skill of 30% crit chance 50% crit damage, AoE hits for 3 times of what he does now. (What an absolute monster once upon a time). Everyone of us in Soft Launch uses him. And have him at 6* or 7*.
Now, Sid lost his past glory, everyone wanted him nerfed, he made DPS teams wipe others in 2 AoEs etc. But they nerfed him a little too much for my liking, losing 2/3 of his damage, reducing 2/3 of his leader skill, basic attack dropped, speed dropped, HP dropped...
Therefore, unless you do not have a decent leader, get Sid first. If you have other decent leaders, get IG-88 first as your glass cannon. And Sid thereafter.
