Zoho Books and Xero were the only invoicing services I found that had all the features I needed (import past invoices, online payment portal, recurring invoices, and invoice customization). After trying both of those, I decided that Zoho Books had much better customer support and was better suited for a small business.
Zoho Books has saved me tons of time. Some of my favorite time savers are:
* Customer statement makes it so easy to send customers an accounting summary of any time range. No more spreadsheet export!
* Customer portal and payment options are simply fantastic.
* Recurring invoices and automatic reminders save me time.
Also, they have great customer support. When a new release resulted in a bug that prevented me from attaching a text file to an invoice, a support rep told me a workaround for it, and the bug was fixed within a few days.
Of course, Zoho Books is far from perfect. The current version has some minor annoyances:
* cannot set a global bcc email (must add it to a bunch of places),
* no easy integration with mailing lists (to email all of your customers that purchase XYZ product),
* and transaction matching is so painful I no longer bother to do it.
But again, those are just annoyances and easy to work around. Zoho seems to be constantly releasing upgrades, and I would not be surprised if all of those issues get fixed soon.