In what order should the Aquarion series be watched?
Considering that Aquarion is an original anime (i.e. not based from other sources), it's safe to say that the original broadcast time is the recommended order:


Genesis of Aquarion (July 2005, 26 episodes): the original story
Genesis of Aquarion OVA (May &amp; November 2007, 2 episodes) / Genesis of Aquarion: Wings of Genesis movie (September 2007): an alternative retelling of Genesis of Aquarion
Aquarion Evol (January 2012, 26 episodes): takes place 12000 years after Genesis of Aquarion
Genesis of Aquarion Evol / Genesis of Aquarion Love OVA (July 2015, 1 episode): featuring a crossover between characters from Genesis of Aquarion and Aquarion Evol
Aquarion Logos (July 2015, 26 episodes): featuring a new storyline unrelated to the previous 2 series.