My favorites for reliable return are the species. There are several forms of T.clusiana, and they're the showiest species I've grown. Brent&Becky's Bulbs and John Scheepers (VanEngelen) offer a good assortment of species, and Touch of Nature offers a few varieties (at excellent prices).
Of the hybrids, the Darwin Hybrids are about the best for perennializing.
Even among those that are better about returning from year to year, they perform best in a location where they can dry out during the summer. They resent moisture during their dormant time.
