tintin for the win.
You can try fiddling around with the settings. Open up the 'Settings' and go to 'Special Options'. Check 'Force telnet GA signal interpretation off'. It may, at least, speed up how quickly Mudlet processes commands.
Also, try adding a new line to the end of your prompt (with the prompt command, you can use '\n' to force a new line) if you use a prompt trigger. That (somewhat) worked for me.