Both brands are perfectly reliable, but, as always, lemons can and will get through the cracks from time to time.
Between the two heads I really don't know which I'd choose. I am personally not a fan of that particular Ampeg head (I think it's one of their worse ones), but the Markbass head is also very new and it hasn't made its rounds on the market yet. I'd say you should check out the Markbass LMIII, Markbass F1, Ampeg Pro7, and Ampeg PF500. All of them are great heads that have their own unique flavor, as well as pros and cons.
If it matters, I own an SVT-CL, Pro7, and the LMIII.