One of the reasons that both AccountEdge and Quickbooks are good options to start with is because they're both software that are sold by big (Intuit) and developing (MYOB) companies. There is lots of accounting software out there to choose from, even for the Mac, but if it's smarter to buy software that is in ongoing development, supported by a significant company, and that offers support for accountants (both of these do).
I went with Quickbooks, mainly because it's a lot easier to find accounting firms that are familiar with the software and can support it. I don't want to have to spend time explaining the new software to the accountant, have to switch on them later when the software is no longer in existence, etc. You want continuity with your software.
I ended up buying VMWare and a copy of Windows for my Mac which allowed me access to Internet Explorer to run
Quickbooks online, and I'm so glad that I did. It allows my accountant to access my account without me ever having to go in to their office, take them backup files, etc. There is already a mini version of
Quickbooks online for the iPhone, and I'm sure that a full version that works in Firefox/Safari is in the works.