We are using Quickbooks at the moment but we will migrate to Dynamics. QuickBooks is a good tool but it is not compatible with the accounting needs of countries other than the US.
The main reason that we are choosing Dynamics is that our CFO knows it very well and he recommends it.
We evaluated many of options including Zoo, Sugar etc., but we finally chose with Capsule. It is pretty straightforward for the simple needs that we have. It integrates well with Gmail and Zendesk.