Fleet

If you wanna go Malevolence of Negotiator then you need to do Geonosis Territory Battles.

Malevolence then needs all the geo pilots as well as Hyena Bomber and Vulture Droid which are crewless. Geos need to be geared up to get Wat Tambor and are a decent GA team.

Negotiator needs JKA, Snips, Kenobi, Fives, Clone Sergeant, Plo Koon and Rex as well as Y-Wing which is crewless. All of those pilots except Sergeat and Plo Koon are necessary for 501st and Padme Teams

Rebels are prolly the easiest to get however they require a lot of gear for B-Grade and below characters like Bistan and Scarif Rebel Pathfinder. They also need bounty hunter ships for Hans Millenium Falcon.

I would go for Rebels if you cant do Geonosis Territory Battles. If you can then choose either Negotiator or Malevolence. Malevolence requires less and more easily available toons geared up but is worse on defence then the Negotiator. Negotiator is the best defensive fleet but requires more and harder to get toons geared up