Yeah; mainly material and mounting. ESP is probably the most beefy one out there(heaviest but probably also the strongest); they're also the only ones using square tubing vs. round. It's what I have on my car. I also had ETD and Avid v2(gave this up due to manufacturing error and didn't want to wait long).
Avid uses only two of the original crossmember mount; replaces tow hook mount, and uses nice Aurora bearings.
Full-Race is probably the "best"; well engineered and quality parts. Though, price reflects it.
Innovative uses the factory crossmember mounting locations(IIRC, doesn't use the tow hook mounts), and uses a rigid mount on the LCA vs. a radius arm with two bushings(the Innovating radius arm is like the stock radius arm with a spherical bushing instead of the rubber bushing).
ETD/K-Tuned-avoid them. I bought this to temporarily replace my Avid due to manufacturing error, and it has cheap bearings/heim joints, L-bracket to use two of the original crossmember mounts(IMO, not as rigid compared to Avid, ESP, and Full-Race), and mine required force fitting/slight bending of the tow-hook bracket.