My daughter swears by Intuit Quickbooks...I myself haven't tried it yet, but I plan on it in the very near future.

I prefer Xero with its ease of use and open architecture. There are many applications which integrate very well depending upon your needs, such as Time Tracking, Job Management and Workflow management, to name a few.

The time I have to devote to collecting bills was cut in half or more the day I started using freshbooks. My accountant uses all the information recorded to do my tax returns. All of my revenue and expenses are automatically pulled into Freshbooks. It's perfect for my business!