I have about 10 crappie rods that are from 6′ super light weight [rated for 1/64 heads] to a 10 footer. I have a pair of 6’6″ rated for 1/32 jigs. I have one 6’9″ ultralight and a 7′ ultralight, plus the two super ultralights mentioned….all of these are custom builds. I have a few St.Croix Trophys too in 6’6″ light weight.
There really isn’t any magic length that is universal. Its about what you are comfortable with. I know people who were talked into 7 foot ultralights that hate the things and never fish them anymore. I know people who simply can’t fish a rod unless its 7 feet long. Everyone is different. Now if it were me, I’d be running down to a FleetFarm or Gander or even [censored] and picking up the ultralights in various lengths just to see how they feel in the hand. I’d even bring a reel along to hang on the rods to see how the balance is and just how well the feel is on each one. I would never buy a rod sight-unseen again. Ever.
People vary, their likes and dislikes vary and then the rods themselves vary even between two supposedly identical rods. Money is hard to come by anymore so I suggest doing some footwork and shop around some to determine what length of rod feels the best in YOUR hands.