People are forgetting each eye has a different affinity. Kakashis was suited for long range, Obitos was suited to close range.
They both showed VERY MINOR control in their "opposite affinity" like when Obito showed he can teleport things he isn't touching when he teleported sakura out from his dimension without touching her (she was a couple feet in front, but still no contact), and Kakashi showed he could teleport himself to the dimension after acquiring enough skill.
I believe with enough practice, they could both master every Kamui skill with just one eye despite each eye having different apparent preferences for their usage, and i think Kakashi is obviously more skilled, but Obito is uchiha, and has Hashiramas cells, and that will put him just above Kakashi.
Plus, Kakashi will go blind, and Obito will not.
As for what we have actually seen them do, Obito has shown greater power and versatility with Kamui by a good margin.