Actually the Mennonites and Baptists can argue authoritatively for as good a claim as that of Rome.
You might try cruising through some of their websites concerning the matter.
As does the Orthodox Churchs.
Say the Greek Orthodox.
Makes sence that God would hide his Universal Church in a little known place unknown to anyone besides for example Greeks. NOT!
Over the last 2000 years what has been the one Church in word and Archtecture that has consistently proclamed the Truth.
You, my friend, need to study the Theology of a leading Calvanist Theologian. He broke with his brothers because they were NOT anti Catholic enough.
He is a PHD of Theology at Franciscan University. His name is Scott Hahn. Here is one of his pages:
http://www.mindspring.com/~darcyj/files/drhahn.html