Spike. In-universe, cuz I’m not sure Thorax is gonna be any good at dominance without an example (weird kinky wrong-sex precedent doesn’t count). From the audience perspective, cuz it balances out the Sunburst (Chrysalis) scene earlier. Maybe Thorax will get a turn later.
This is a tough question so I flipped a coin and so I’m going with Thorax, but I will be fine with either one… and It’s a good thing that Thorax is staying himself, don’t want another bot situation i guess…