Here at Beaches Electrical Service Inc, we use Quickbooks Online for our invoice, billing, payroll and accounting.  Having the ability to create and send invoices while on-site is a huge advantage over the previous system of using hand written estimates and invoices.

However, if you don't need the payroll services, then I could suggest XERO (https://www.xero.com/us/)which is a less expensive, easy to use online accounting software.