Formal:
* Mi programa de televisión favorito es... (My favorite television show is...)
* Me encanta la serie... (I love the series...)
* Adoro la serie... (I adore the series...)
Informal:
* Mi serie favorita es... (My favorite series is...)
* Me fascina la serie... (I'm fascinated by the series...)
* Amo la serie... (I love the series...)
You can also use a combination of these phrases, for example:
* Mi serie favorita es "The Walking Dead" porque la amo. (My favorite series is "The Walking Dead" because I love it.)
Remember to replace "The Walking Dead" with the name of your favorite show.