Is Ripple centralized or decentralized? Are people still fighting about this or have they come to a consensus? Also, as of today (Sep 2015), what is the main advantage of Ripple over Bitcoin?
According to Ripple: Ripple for Financial Institutions
Financial institutions, network operators and regulators play critical roles scaling and providing stability to payment systems. Ripple enhances the existing payment stack, offering real-time settlement infrastructure at the foundation."

https://ripple.com/integrate/

Given that financial institutions, network operators and especially "regulators" are part of this equation then in this instance of "Financial Institutions" when considering the totality of human involvement it perhaps could not be considered decentralized, which in the context described makes it centralized.

Ripple also states "Jurisdiction or network specific rules, governance, standards, and other critical functions are intended to be provided by existing systems and operators."

With respect to your second question Ripple is a system for exchanging the Internet of Value (many different assets digital and physical) in which they also offer their own XRP digital "currency", whereas Bitcoin is simply another digital currency.