Sol or Amaterasu+ any other SSR kami is what ppl usually aim for, depending on luck and you patience it might be impossible to achieve.
So you could settle with SOL only or a combination of 2 SSR kami of the same element, otherwise any combination of 2 Kamis you like are good if you plan to buy the SSR pick ticket down the road for SOL, otherwise a single SOL would probably benefits you more in the long run because it will synergize with any SSR you will ever get.