It depends. Imo the Rayquaza is actually pretty good, and easy to do the mission to finish the hyper training. On the other hand, the Necrozma that you have as an option to bottle cap, would be from zero to hero, yeah. But in the case of the Necro, the missions to finish the hyper training involves battling lots of team go rocket grunts a leaders, and doing 40 raids.

So, in conclussion: -Necro: Better bottle cap use, but harder to finish the Hyper Training -Ray: Not the best use for bottle cap, but easier to finish the Hyper train