Who is FIS' biggest competitor?

As an expert in the world of finance and cryptocurrency, I'm curious to know who FIS' biggest competitor stands as? With the rapid advancements in the digital payments and financial services sector, competition is fiercer than ever. Could you elaborate on the company that poses the most significant challenge to FIS, detailing their strengths, market share, and any unique offerings that may set them apart? Understanding the landscape of their competition is crucial for any business looking to stay ahead in this dynamic and competitive industry.