What is the most common protocol?

When it comes to the realm of cryptocurrency and blockchain technology, there are numerous protocols that underpin various networks and platforms. But, I'm curious to know, what stands out as the most commonly utilized protocol in this dynamic landscape? Is it the one that prioritizes speed and scalability, or perhaps the one that emphasizes security and decentralization? I'm eager to understand the rationale behind its prevalence and how it has shaped the development of the cryptocurrency ecosystem.