I am initiating my coverage of ACI Worldwide (NASDAQ: ACIW ) with a ‘Buy’ rating for long-term investors primarily due to their mature business model, expanding margins, and modest relative valuation despite 100%+ appreciation in their stock price over the last year.Analyst’s Disclosure: I/we have no stock, option or similar derivative position in any of the companies mentioned, and no plans to initiate any such positions within the next 72 hours. I wrote this article myself, and it expresses my own opinion ...