"Disorder" might be my favorite Joy Divison song.
Hard to pick a favorite New Order song since they had so many different eras and styles. "Ceremony" is the best of their classic post-punk works. "True Faith" was an incredibly influential song musically despite being less-known. "Temptation" and "Sub-Culture" are works of art.
Picking favorite New Order tracks is especially difficult since many of their singles have multiple mixes, with substantial differences. For example I always prefer the gothier 12" remix of Sub-Culture, or the dancier Shep Pettibone remix of "True Faith". And meanwhile with some hits like "Bizarre Love Triangle" there are far too many versions to even keep track of...
There are a lot of great covers of the tune. I love Dean Wareham's. Every time he plays it, he seems to find something new.
His cover tends toward melancholy. Peter Hook's, a little angry, sometimes triumphant. There's a cover by Day Wave that's almost happy. Several ambient covers that range from, I dunno, anhedonic to transcendent.