Why Spencer Should...

Anastasia is Spencer’s best option for the team swap because she would cause the most chaos among the red team. She’s an explosive and stubborn person, who doesn’t back down easily and is hellbent on winning. Anastasia already has friction with Ivy over dislocating her shoulder in episode 7, so they’re more than likely not going to get along. There’s also the fact that Ivy and Zaid are willing to sabotage the team, which isn’t going to sit well with Anastasia, who will lose her shit once she finds out they're costing them challenges. This will provide Jade with the perfect distraction because all the attention will be on Anastasia instead of her.

Now Isabel can save Jade with her idol, but there's no guarantee she'll want to do this. She could be against the idea and want to save herself and get rid of Jade, who she considers a threat. Also, if the merge happens at 8 contestants, then Jade is still in danger of elimination because there will be two more ceremonies on red team. Isabel can only use her idol once to save Jade, which will leave them at a disadvantage afterward because they still won't have voting power. If Isabel stays on the blue team, she and Spencer could become allies, working together with Natalia, Logan and Richard.

Anastasia can put the red team in a vulnerable position, which will benefit Spencer, who wants his former team to be as weak and distracted from Jade as much as possible.