Best months = March, April and May, because its above freezing most everywhere, so no frozen plants in the mail, and the plants are just beginning a new growing season, its Spring, and they still have a full season, (plenty of time), to prepare for dormancy the following winter.
February would be fine in the south, but not the north.
(can get frozen plants in the mail in the north)
February can be considered REALLY early spring in the south,
fine for getting a new VFT.
Worst months - Sept, Oct, Nov, Dec, Jan.
because its autumn and winter, and the plants should be nearly dormant (autumn) or fully dormant (winter)
Summer is ok..but not ideal, because there isnt much time to prepare for dormancy.
although if you know you are ordering plants from a nursery that has been keeping the plants outside all season, then ordering in the summer would be fine..because they will be going from the nursery outdoors to your place outdoors..
not a major difference for the plants.
best - Spring
ok, but not great - Summer
bad - Winter
the worst - Autumn
Scot