We had issues with quickbooks running payroll randomly and paying to accounts we didn't expect - not fun. ZenPayroll is stupid easy, clear, and they deal with IRS and backend pieces you shouldn't have to spend your time on. Hurrah for the product that doesn't suck!
We use it at BookInABox. It's pretty remarkable, how good it is. We actually study the workflow and decision trees of our payroll software and learn from it, that's how good it is.
Pitch Drone