I think the next choice is Cummins. If not then Smith. They are our best two players who can command respect from the players based on their personal performances.
Labuschagne is a fair way off I think. I'm not sure he has the total respect of the playing group right now (If his on-field antics are anything to go by). If anything you'd let him captain some throw t20 matches to see if he actual has any tactical nous.
However I agree with Ponting. At this stage Paine is captain until the Ashes. But he has to learn from his mistakes if we are going to win against SA or England. Judging on his record he doesn't learn much at all.
This upcoming 3 test match tour of South Africa is Paine's last chance as test captain, and by the end of the tour, the selectors will have had more than enough time to figure out who they have penciled as Paine's successor.
As much as I'd like to see Paine dropped right now, based on the responses in the media on the subject of the test captaincy from ex-players, the uncertainty and confusion over who should succeed him as test captain is the only reason why Paine will still continue in the team for the South African tour.
If Australia fails to qualify for the World Test Championship final (which should be the first and most important priority between now and the final in June), Paine's captaincy role should be immediately stripped from him after the South African tour, and big changes need to be made in the overall squad before the Ashes next summer so we start the 2021-23 WTC cycle on a strong note.
From now until the end of the Shield season, selectors need to also focus on who they have in mind for the Ashes squad (assuming COVID bubbles/hubs still remain by end of year, meaning there will at least be an 18 man squad in the hub like there was for this recent test series vs India), and not wait until the last minute just before the first test match to see if a bolter will emerge in the 3-4 Sheffield Shield matches that are played before the Ashes (like they did this summer with Cameron Green).
This season's Sheffield Shield season will finish in mid-April. After the Shield final, selectors should have a list of 25 players who they realistically could see playing in the Ashes. Play three Australia vs Australia A 4/5 day matches around August-October (consisting of those 25 players), with the top 18 making the final Ashes squad in November.
