The 3D glitters (gold, silver, copper and lustdust - if it can be included in this) have a rainbow effect. The gold, copper and lustdust ones that i have are small in glitter size, whilst the silver is large (and thus you notice the rainbow effect more - though i think that i just have the old silver. Im pretty sure they were all reformulated to a finer glitter). These are my favourite MAC glitters, and go with pretty much anything.
As far as i know, the 'reflects' are very fine glitters that reflect the colour they are called (ie reflects gold is a white glitter that reflects/flashes gold).