Type 1: The Greys - These are the most popular type. They have big black almond shaped eyes. They are believed to be from the Zeta Reticculi star system. Their experiments often include removal of fetuses which female abductees don't remember being pregnant. It seems that the greys tend to act in a collective manner. There are arguments of whether they are insect or amphibiain.
Type 2: Nordics - Probably the most humanlike aliens are the Nordics. They seem to be against the greys or at their side. They are muscular and attractive. The peak of reports of them happened in the 1950s and resemble the movie stars of that time. They have blonde hair and, in some cases, have had sex with the experiencers (Such as Antonio Villas Boas). The most famed contact with the Nordics happened during the 50s as George Adamski reportedly made contact with Venusians of that description. Some people believe they are the guardians of the Earth.
Type 3: Reptoids (aka "Reptillians") - The most aggresive type of alien reported so far seems to be a reptillian version of the greys. They seem to be the leaders of the greys and are believed to desire the takeover of Earth. They are said to regard us as food. Their likeness in behavior to the "visitors" from V: The Series is also widely noted. If you want to read my science fiction story about this species, Click Here.