Ina, because Kiara is entering the "moving back home" arc and it will hurt her growth. Anyone's guess what happens after 1 mil though. I would not be at all surprised if Kiara did another "sing till 1 million" stream which would potentially help her close the gap.
I think it'd be cool if Ina and Kiara were both coming up to 1 million around the same time and did something together, be it a joint celebration, or even a duet karaoke "till 1 million" would be cool. Even though Ina probably wouldn't do that on her own I can imagine Kiara talking her into something like that (the way she talked Gura into doing a 2m celebration). I generally would love to see Ina and Kiara celebrate the milestone together somehow, cause I think they have good chemistry together. The 4chan threads would be awful though with Tako shitposting, unfortunately.