| Personally, I don't think "mutated" seeds are the problem... unless you are referring to GMO's, which are unavailable to gardeners. Did you perhaps mean hybrids? As a member of the Seed Savers Exchange, I am certainly no fan of hybrids, especially those bred for commercial production. Those varieties are bred primarily for traits useful to the industry (such as ease of harvest, long storage, and appearance) not flavor & nutrition. My criticism of hybrid garden seeds, however, is mainly that they have forced many equally good OP (open-pollinated) varieties out of the market. While some hybrid vegetables may be nutritionally deficient as a result of their parentage, there is no guarantee that OP vegetables will perform any better. Whether hybrid or OP, there are both good & poor varieties in each category. The problem is that reliable, variety-specific nutritional data is hard to find. The USDA has done testing on some of the edible plants in their collection, so if an OP variety can be found in their listings, it might give some useful info. But it's worth noting that the way in which a vegetable is grown has at least as much influence over its nutritional content as its genetics - and maybe more. The reports that I have read of declining nutritional values seem to indicate that it is not hybrids themselves that are responsible, but the depletion of soil nutrients by non-sustainable, chemically-dependent agriculture. As gardeners, we have more control over our soil than most farmers. I'm a firm believer that if you feed the soil, the soil feeds the plants, and the plants feed you. Heirlooms do their best when grown with the organic methods that they were selected for... just as hybrids may excel when grown with the chemical methods they were selected for. You can learn more about improving soil fertility on the Soil & Compost Forum, and the Organic Gardening Forum. There are many "Best heirloom seed company?" threads on this website, with extensive lists. Besides Sand Hill listed above, I have had good results from Victory Seed, Baker Creek, and Seed Savers Exchange (the catalog). The most comprehensive list of heirloom/OP seed is contained in the SSE publication Garden Seed Inventory, Sixth Edition. It's a little outdated, since it was published in 2004... but in the front of the book is a listing of all U.S. & Canadian companies that sold OP seed at the time of publishing. It is still my #1 source for locating commercial seed sources. You might also want to check out the Cornell University site "Vegetable Varieties for Gardeners", which not only provides links to sources for the varieties listed, but has reviews of their performance by other gardeners. | 
