If the RAM is certified for the MacPro, 08 or others, and has a lifetime warrantee, there is currently no difference in performance between brands.
Barefeats.com has done several RAM tests with different brands and memory card configs, and to get the best 8G performance in a 08 MacPro, you want eight 1Gig sticks to fill all the RAM slots.
You will not find a RAM vendor that has never had a RAM fail, and they all seem to have about the same, very low, failure rate. You may want to ask how the customer service compares... DMS ships out replacements as soon as you call them, no questions asked, others may do the same.