Personally, I have never found very much difference. The difference between catalogs is the amount of variety/diversity. If you are looking for something unusual, rare, heirloom etc, some catalogs are better than others for finding it. But if you are looking for a Better Boy tomato, it doesn't matter where you get it from.
I have used a variety of catalogs: Jung Seeds, Park Seeds, Pinetree, Johnny's, Territorial, and others. When I was starting between 500 and 1000 plants from seed each year, I used HPS Seed. They sell seeds in bulk quantities. Instead of getting a packet of 30 seeds for $2 (or more) from a regular catalog, you can get a packet of 500 for $7. (If you are really a commercial grower, you can also get a packet of 2500 seeds) Since seeds almost always last for three seasons, if not more, I just saved the extra for the next year.