List of User's Comments - show one latest comment on node only
I would use the Views Field View or a similar module for this.

The reasons is that you are trying to filter on two things:
* Most recent comment
* Unique node

I would create a "parent" view that shows all nodes the user has commented on and then a "child" view that filters the comments on each node to show the most recent one.

See my detailed answer here to a question about getting the latest node per user.

An alternative is to play around with Views aggregation settings.