Ekaterina, definitely. Because they are the smartest of the Cahill branches and can invent almost anything.( Example- they invented the atomic bomb! Isn't that just awesome?) Need I go on?
This is what I found on a website.
I think that the most likely choice is that Amy is a Madrigal and Dan is a Ekaterina. This is the way they strike me in; with Dan being smart and inventive; experimenting. Amy even called him a "natural Madame Curie," who happens to be an Ekaterina.
In book six, Amy definitely proves she has Madrigal ability by tracking for trails; even though I'm pretty sure she's never been taught that.
So I think Ekaterina is the best! Because Madrigal is not really a main branch.
The Ekaterinas
kabras branch leaders Is the answer (39 clues winner)
The Holts of the Tomas branch are the muscle people in the 39 clues.
You become a madrigal by completing Mission 10 on the 39 Clues site.
Lucian.
Tomas
Amy and Dan Cahill are part of the Ekaterina branch in the 39 Clues series. The Ekaterina branch is known for their intelligence and passion for knowledge.
Tomas
u cant
madrigal
Grace is a Madrigal.
Tomas the name of his branch