Supernatural

I finished the season 10 serie Supernatural. I thinking this is the best series.

A couple of different ways:

(most natural to me)

I finished season 10 of Supernatural. I think this is the best series.

(also technically correct)

I finished the 10th season of the series Supernatural. I'm thinking this is the best series. 

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Hope it helps : )

I finished the tenth season of Supernatural, I think it is the best show/series.