What is the most logical response to phrase Que tal?

The most logical response to "Que tal?" depends on the context and your relationship with the person asking. Here are a few options:

Formal:

* Bien, gracias. ¿Y usted? (Good, thank you. And you?)

* Muy bien, gracias. ¿Y usted? (Very well, thank you. And you?)

Informal:

* Bien, ¿y tú? (Good, and you?)

* Más o menos. (So-so.)

* Todo bien. (Everything is fine.)

If you want to be a bit more conversational:

* ¿Qué tal todo? (How's everything?)

* ¿Qué tal la vida? (How's life?)

Important Note: "Que tal" is a very casual greeting, so a formal response might sound a bit odd.

Ultimately, the best response is the one that feels most natural to you and fits the situation.