Magento is still in Beta, so I wouldn't advise using it in a production environment yet. They expect v1 to be available Q1 2008 so if you can hang on until then, it might be worth giving it a go, though I imagine it'll still have one or two bugs that'll still need to be ironed out even then.

If I was going to start a new store now, I would use Zen, if I was planning to start one next year then I would use Magento.

__________________
Lawrence