I would definitely go for Asus. Quieter and cooler. And I definitely trust Asus more. Have yet to get an Asus video card fail on me under 5 years of usage.
And is a Zotac a reliable brand? Maybe. For some higher-end models, they do a descent job. But if you take a look at their GT line - they fail horribly. Got a PC technician and he has a nice box full of Zotac GTs failing within 1-2 years. That box's size is a bit larger than all the other boxes with Asus, Gigabyte, Sapphire combined. I don't like a brand that only puts effort in the expensive cards - because there is the media coverage.