I just ran a few months with Quickbooks, Xero & Wave.
I chose Quickbooks for various reasons even though it is twice the cost of comparable Xero product. (Wave is Free)
And the only thing that kept me in limbo of using Quickbooks was this HORRIBLE Invoice email.
My work-a-round is to either
1.) email the invoices to myself and then I forward them to my client with my own email template
2.) always choose "send later" and just download the .pdf and email that to my client.
(again, I could use a locally saved email template or starter email from my outlook)
The big question is why can't we just edit this. The email content shows up in the customize window.