I have ordered bulbs from a mail order nursery often because they offer species or cultivars that the local nurseries don't. But mainly I get mine at Lowe's.
I've ordered bulbs online mostly. I've tried some from the big box stores, but they didn't seem to be of great quality or have a good variety.
I didn't participate in the poll because I prefer to trade for them. Stores do not have the ones I would like to have, and most of the traditional spring bulbs at BBS's are not suited to a permanent life in the deep south. Bulbs are my favorite kind of plant for outside decoration.