I have Seasons 1 on DVD and Seasons 2-5 on Blu-Ray. I was almost going to get Season 1 on Blu-Ray one day but I decided to do it another time but I like the later seasons better. My favorite seasons are Season 4, 5, 6, and 7.
Season 4: Story Line getting started
Season 5: Story Line Begins
Season 6: Getting deeper in to the story!
Season 7: Getting more deep in the story!