I've tried them all, and been involved with dozens, multiple times.
NOS Mopar firm feel -- sweet. Effort increase on highway maybe 50-75%.
Parts store (most are actually A-1 Cardone) - sloppy. Tighten the lash, they go numb. Lousy, period.
FFI knockoff, from place in Ohio - More effort, otherwise, see previous comment!
Genuine FFI St. 2 - Even better than NOS. Coupled with increased caster, a bit of a reduction in line pressure, 11/16" tie rods, bumpsteer blueprint, drives like a modern rack/pinion car.
Rick