Best to worst:
Season 5
Season 2
Season 1
Season 3
Season 4
Season five had everything that made a good season. Actually it was like a big movie or something. There was no episode I didn't like. It had very sad and dramatic moments, funny moments, new, fresh characters (Rachel, Tom and Renée) and a great storyline that was full of twists.
Season two was also great because of the great storyline with Irina and Sloane, but for me it was almost as good as Season five was.