If you're really looking for quality, then you want to go with Bosch 20 mm.
Bosch Rexroth:
3m of 20x20 for $20.00 (no discount)
I = .67 cm^4, (.016 in^4)
W = .4 kg / m, (.269 lbs / ft)
Pullout = 1700 N, (382 lbs.)
Tensile Stress = 250 N / mm^2
Item:
3m of 20x20mm for $25.50 (discount)
I = 0.72 cm^4
Weight = 0.48kg/m (.33lb / ft)
Pullout = 500N (112lbs.)
Tensile Stress of Aluminum = 245 N / mm^2
I'll leave the choice up to you.
It's considerably lighter, just slightly less rigid, about 20% cheaper, and has better fasteners.
Hope this helps. Good luck boys and girls!
Matt