Dahlias are such obviously beautiful flowers that they will look good in pretty much any photo. No matter the lighting or composition, a dahlia will always show its beauty. It is a bit like a fireworks display: it always looks somehow nice, even when we are not in the best viewing spot or the weather is a bit foggy.
Pentax K10D + Zeiss Sonnar 85/2.8 + extension tube + off-camera flash
Hibiscus, on the other hand, are not so spectacular. These are more discrete and sober flowers, demanding some care and subtlety in the way one captures the image.
I think these two situations also occur with human portraits...
Pentax K10D + Zeiss Sonnar 85/2.8 + extension tube + 2 off-camera flashes