As of now, none of them are strong enough to be kage but both have a potential to become strong enough to defend the village in a few years.
Well firstly speaking, Shikamaru was made commander of the 4th division. Then he was forced to leave that division along with Choji to support Darui's division. Now it was never declared that Temari became the commander but from the looks of it, she was technically the commander since she was giving orders to her division. It also logically makes sense because there was no one else on her division other than Dodai who was up to the task but since Shikamaru was first made the commander, I am inclined to think they'd choose Temari as the one to replace him.
Well the reason why I think Temari would make a better Kazekage is because I think Kankuro should lead Suna's army or some special ops since he is good at that kind of stuff. I don't think he is very diplomatic or political because he can come off as some jerk such as when he bullied Konohamaru. Also she is smarter than Kankuro based on the data book, her age and my personal opinion based on how both were shown in the manga. Temari was also made the ambassador to Konoha and was the teacher at Suna's academy (according to data book) so she has great leadership experience as well.
Also during the beginning of Shippuden, Kankuro wrecklessly chased after Sasori and I believe Temari would be wiser and more cool headed than him in that situation. Also some people tend to think Temari is a hot headed person which is not true. As a matter of fact, Kishi's own words say that Temari never panics even in a moment of crisis. This is the type of person we need as Kazekage or any kage.
Also if a mob of enemies were to attack the village, Temari would be more suited to defend it because her attacks cover a wide range and she has an ultimate weapon capable of destroying everything in a vicinity of hundreds of meters.