When someone says, "You are my favorite," the best reply would depend on your relationship with the person and the context of the conversation. Here are a few possible responses that could work:
Thank you! That means a lot to me. You're one of my favorites too!
Aww, that's so sweet of you to say! You're pretty awesome yourself!
I feel incredibly flattered! You're definitely one of the best people I know as well.
Wow, I'm honored to be your favorite! I'm lucky to have you as a friend/partner/family member too.
The feeling is mutual! You've always been a favorite of mine as well.
Thanks! Your support and friendship mean the world to me.
I'm grateful for your kind words. You're one of the reasons I enjoy spending time with you.
Remember, the key is to be sincere and appreciative in your response. Tailor your reply to match your personality and the bond you share with the person who said it.