I've read a long time ago that square tubing is stronger than round tubing, if you keep the wall thickness the same. Round tubing does take up less space however.
If it?s street only, then it?s really up to you. Pretty much anything from any reputable company, such as Griggs Racing, Maximum Motorsports, UPR, D&D Racing, and others will work just fine. I don?t know about drag control arms, but most of the road race control arms are heavier than stock, just so you know.
Wow man, I just started a thread on this very subject over on Stangnet. I havent received many replies though. Im leaning toward tubular, as the inexpensive boxed ones seem like they would be thin metal... Thats probably just in my head though.
I don't think it's a matter of boxed vs tubular, but a question of how it's formed and what materials are used; regarding strength. As far as the application goes, what type of bushings being used or should spherical bushings be used? I personally would not be concerned with the shape.