Shredder gun is nice but the guided blaster bombs are insane with their super long range (up to 45 I think) and a large radius and damage.
I'm a big fan of PSI Ops but would go GWC > Proving Ground > AWC > PSI Lab
GWC is awesome for increasing squad size and vulture to get extra loot
Proving Ground is awesome for upgraded grenades, heavy suits/weapons, and spider suits
AWC is awesome for faster healing but also for the bonus abilities which you'll miss if you delay it too long. Each soldier has a secret bonus ability unlocked at a certain rank and if that rank is achieved before the AWC is built you will never get that bonus ability unless you cheat with the AWC mod that alters how it works.
Some bonus abilities suck "Salvo on a specialist? lol, he always carries a skull jack and medkit so wtf" but there are so many incredible abilities that are amazing like Holo Targeting on a Specialist or Sharpshooter, Rupture on anyone, Shadow Step on a Specialist/Grenadier, Kill Zone on a Specialist, Guardian on a Sharpshooter, and so on.
Here's a list of the bonus abilities the AWC can grant. Some are meh but some are amazing.
http://xcom2.wiki.fextralife.com/Adv...Warfare+Center