There is no best species. Different species of phytoplankton are more easily consumed and digested by different forms of sea life. It is best to give your captive reef a broad variety of feeding options. This increases the biodiversity, more closely mirroring natural seas and reefs.
Phyto2 will smell sour and sulphurous and the cells will clump into large chunks and masses (.125" or larger) on the bottom of the bottle. AZOX, NAUPS, NAUPS-D, Rotiplex and S.E.L.C.O. BOOST will show no difference and should be disposed off after 14 months.