I have ordered through many catalogs over the years for seeds, and I have never had a bad bunch from any of them, or a problem with an order. I buy most of my seeds at the local garden store or Meijer (usually Hart and Ferry Moss), and order the rest from various places, but from Jung's more often than not. I usually order bulbs from Van Bourgondien, and like other places I have ordered from, have never had an issue with their quality or the ordering/shipping process.
I have not ordered live plants, so I can't give advise on those.
My bottom line is, I believe most mail order places that have been around for decades have quality seeds and bulbs, they couldn't stay in business if they didn't, and you can expect 'decent stuff' from them. Most posts I have seen that put down one vendor over another stems from a bad experience with customer service, rather than poor quality products.
Stokes, seedsavers.com...most of my seeds from Stokes this year. I researced a ton this past year and they have good stuff, not owned by one of the major owners. Seedsavers is very good. HIghly recommend both!