Based on current form?
It's Araujo, Pique, even before his injury was a bit sloppy and Inconsistent but nowhere near as catastrophic Lenglet has been this season. For me, the ranking goes.
1 Araujo
2 Pique
3 Mingueza
4 Lenglet
5 Umtiti
I'd rank Mingueza close with Pique though, been great and had some sloppy moments but otherwise a surprise revelation this season. Lenglet should hang his head in shame for his current form, He's making mistakes you would expect the likes of Mingueza and Araujo are due to their inexperience and age but Lenglet is 25 years old and has been playing top-level football for far longer than these two have.
Umtiti will remain in 5th place, sure he will show some quality moments on the ball but the guy is done for the most part.