In general, evergreen types will do better in hot climates with very mild winters and dormant types prefer colder areas. Both types will grow in South Carolina. Tetraploid daylilies have twice the normal number of chromosomes. They have larger flowers than most daylilies. Colors are often more intense.
Scapes tend to be sturdier and stronger.
Diploid daylilies are considered by some to be more graceful in form. Spider and double daylilies are more commonly diploid. Diploid flowers though usually smaller are also more numerous per plant. There are more diploid daylilies than tetraploids. Everblooming daylilies bloom repeatedly through the summer and may have very little or no time between flushes of bloom.