I've found soft necks pretty easy to grow here in Nebraska. Really haven't noticed any difference in winter hardiness between the softneck and the hardneck varieties I've tried.
Friends who just planted garlic cloves from the grocery store were less than happy with their results, however. I suspect that the garlic we typically see in the grocery stores around here is from a handful of varieties grown in California and/or the Pacific Northwest. Given the nature of modern agriculture, it wouldn't be surprising if those varieties were highly productive under the right conditions, but not very adaptable.
