To be honset, I haven't bothered with season 5 since it originally aired. I did not feel incnlined to get it on DVD with the rest of the series.
But this is not about my history with EFC. I only bring that up to point out that my memory of the season is extremely hazy to the point of being non-existent. But I seem to remember Boone's Assassin, the one where Zo'or is resurrected as an Atavus and sent to kill Boone as actually being half-decent, so I'll vote that as the best of the season.
But, man, most of the time the show was just "Atavus hybrid chamber of the week." This week it's in a hospital, a health spa, a high school. What a painful year.