Chose Email on Acid
Email on Acid has more features than Litmus. They offer more email clients to test on and during my time using both tools, had fewer clients that displayed as being down. This was a major time suck especially when testing for specific clients such as Microsoft Outlook.
Independently Invited by TrustRadius
A de minimis incentive was given to thank the reviewer for their time. The incentive was not used to bias or drive a particular response, nor was the incentive contingent on a positive endorsement. More Info