From the ever popular CNCZone:
Al_The_Man and Crevice Reamer:
Only 3 types of couplers offer true zero backlash connection:
Solid. (which can cause problems unless PERFECTLY aligned, Helical, or Oldham. Helicals are basically solid couplers with some alignment flexibility. Make sure you get the clamping type.
If by Lovejoy you mean spider type then it depends on what material and fit is used for the spacer, the next best is Oldham which is a form of zero backlash spider style.
There is also Disc type zero backlash, if using Helical for any kind of stepper or servo torque application then stainless should be used, aluminum does not stand up to repeated flexing, especially with any slight misalignment.
Either the Lovejoy or Misumi sites will show all the different kinds they offer.