There are lots of nice features in Harvest and I tried it out briefly because it has project tracking, but truthfully I'm still a huge fan of Freshbooks and after a few weeks of working with Harvest I came back to old faithful,
Freshbooks <affiliate link> especially since they've not included budget tracking against projects.
I agree with you their response time was great when I was trying out the service, but the one thing I found lacking was the ability to integrate different payment gateways which I love about Freshbooks, so my client when they receive their invoice they can simply make a payment by clicking on a button with in their invoice.