Messi has continued to score goals for Barca, but is struggling to match the spectacular form of Ronaldo in the closing weeks of the season.
"Cristiano is the best in the world. We are fortunate to have him. Messi is different and I stay with Cristiano - and not because I am in the Madrid team."
On his own future, Ramos adds: "I would sign with my eyes closed a contract that allows me to play out my career in Madrid. I talk a lot to (Real president) Florentino Perez and hope we can stay together for another two years."