What is the best Kellogg diagramming software?

Hi everyone!

I am a tutor seeking advice regarding sentence diagramming software. I teach international ESL university students and have found that many find diagramming sentences a more effective learning method than other methods I have tried (perhaps this is because diagramming sentences does not involve even more words?) Anyways, I am currently browsing the wide selection of diagramming software on the web, and would love any advice on what seems to be the best value.

Thanks so much!

Which have you used?