Here are the rewritten sentences:

6. John is the smartest person I’ve ever known.
I have never met anyone more intelligent.

7. Joanna is the top student in my class.
No one performs better than her.

8. I like listening to music more than watching TV.
Listening to music is more interesting than watching TV.

9. Life in the past wasn’t as comfortable as it is today.
Life today is more comfortable.

10. This comic book is more engaging than that novel.
That novel is less interesting than this comic book.