In case it hasn't occurred to anyone yet (it only just occurred to me): did you know that you can use Logos' Sentence Diagram tool to create argument maps?
You can be more creative:
The only downside to using Logos is that it is not as quick (drag and drop) as argument mapping software that is designed specifically for argument mapping. This matters a lot when you're making very big maps. For instance, here is a typical small map for my purposes:
Creating something of this size would be more cumbersome in Logos. But I wonder if, since Logos already has the basic framework down, they might not improve upon it and even make more flexible for diagram arguments and not just sentences?