Looks like the `ets` readme has a direct comparison:
> The purpose of ets is similar to that of moreutils ts(1), but ets differentiates itself from similar offerings by running commands directly within ptys, hence solving thorny issues like pipe buffering and commands disabling color and interactive features when detecting a pipe as output. (ets does provide a reading-from-stdin mode if you insist.) ets also recognizes carriage return as a line seperator, so it doesn't choke if your command prints a progress bar. A more detailed comparison of ets and ts can be found below.
> The purpose of ets is similar to that of moreutils ts(1), but ets differentiates itself from similar offerings by running commands directly within ptys, hence solving thorny issues like pipe buffering and commands disabling color and interactive features when detecting a pipe as output. (ets does provide a reading-from-stdin mode if you insist.) ets also recognizes carriage return as a line seperator, so it doesn't choke if your command prints a progress bar. A more detailed comparison of ets and ts can be found below.