Well, we have one big constraint which helps us to narrow down the candidates and makes our variety selection easier: our climate. We have scorching hot summers with frequent droughts and nighttime temperatures in the mid-70's (some plants, notably tomatoes, will not set fruit if they don't get to cool off enough overnight). Plus some very robust insect populations due to the generally mild winters and early spring. Paradoxically, our summertime daylight hours are shorter than in areas further north, so that the plants don't get as much light energy with which to grow, produce, and stay ahead of the pests. So the number of suitable varieties is greatly reduced.
This month we made our selections and placed four seed orders, all within about a week. These orders, plus the seed leftover from last year, should get us through most of the year, though we will probably order a few more varieties for the fall growing season. We ordered from Johnny's, Tomato Growers, Territorial, and Baker Creek. All the orders have arrived; we now have a container full of seed packets in our refrigerator.
Take a look at these beautiful seed packets from Baker Creek:
Can't you just taste one of those Green Zebra tomatoes? I hope ours look like that.