AccountEdge Pro is the most robust accounting program for the Mac, with full inventory capabilities, integrated payroll, robust job costing for construction companies, retainers and escrow accounts for lawyers, built-in multi-currency,and a third level of transaction categorization in addition to jobs and categories (classes) called departments. It also has a Windows version which is free to accountants that is virtually identical and files from the Mac can be opened on the Windows version without conversion and vice versa.
That said, it doesn't mean it is the best option for all businesses that are using Macs to run their business. Other options are AccountEdge Basic, QuickBooks for Mac, QuickBooks Online, Xero, Wave, and Sage One, to name a few. So it depends on the type of business and what they need to run the business.
AccountEdge Elite Certified Consultant, QuickBooks Advanced ProAdvisor, QuickBooks Online ProAdvisor, Xero Certified Consultant, and Sage One Partner