Acoustic Guitar Construction

There's a whole bunch of truss rods offered by a whole bunch of vendors. And prices vary. Are there significant differences among them? Any truss rods particularly well-made, easier to adjust or more effective doing their job? Is the location of the adjustment nut a cosmetic choice or does one configuration work 'better' than another?

Thanks, folks.

I am only one guy that has repaired guitars -- but I have never seen a neck problem that needed or could be repaired via a two way truss rod -- so my choice is the nice light, stable, durable alumimun single action U-channel, there is also a two way version. As for the two-way opposing rod/bar models, get a good quality unit and even then I have read but not confirmed that the welds have failed on even some of the most popular ones sold today. So I'd at least make sure its a nice clean bubble free weld and for sure I would not use a rod with a brazed or silver soldered adjusting nut connection.

Thanks for the view from experience. Good advice about the welding, too. Nobody wants to see a truss rod a second time after it's installed.