We got our first plants from wherever, but the last two years the best tomatoes came from Papa Geno's Herb Farm. The plants were quite healthy and thrived in the SoCal sunshine. Miracle-Gro probably helped, but it did make the plants a little leggy at first. ;o) If you're in the US and looking for a good heirloom to transplant, they're a good source.
This year, of course, we can't have live plants shipped. So I'm trying seed, and we'll see how that goes. We're buying from this place this year. I like what they do even if their politics suck towards GM foods. Tomatoes, peppers, basil, and maybe a watermelon, if I can figure out where to plant it.