If you’re also considering what you can bring to the party, almost anything can be good.
What could work:
Linker 2 - 2-3 more links, which also helps with your cannon. You’d also be sharing your Quick Cast (without attribute)
Kino 1 - Swap + Teleport allows you to skip some stuff in dungeons. Swap can work as sort of a pulling skill for bosses, allowing you to move them back into someone’s land deployment, or even yours if you’re taking Warlock at R7. Teleport supposedly removes agro from yourself, passing mobs to your Shogoth. And to a lesser extent, use Telekinesis to hold a linked target inside an AoE
Thauma 1 - +218 atk for the whole party
Sorc 1 - it will mostly be for Servant, which is good for your Flesh Cannon, and Familiar, which does ok damage at level 5 but works great with Links
Chrono 1 - People usually you either go Chrono 3 or Chrono 0, but Chrono 1’s an ok filler too for Physical-DPS heavy parties. With just Chrono 1, you already have a 25% crit buff, a crit resistance debuff, and whatever it means to reduce chances of nullification (anti-block/dodge?). And you’ll also have the same level of Reincarnate and Stop as a standard Chrono 3
Cryo 1 - Freezes are quite unreliable
So I think it’s just up to your preference
As for Necro 2 vs Warlock, I’d go for Warlock