Capture Approver and Comments for each Flexi Task reponse

I can't say which one is best, we can pick the one most suitable for the requirement. Below are the possible 3 options I see (2 are already mentioned by you).

1. Use All Approver Comments / All Approver Comments (HTML) references from Common section. We can use it in emails / to save, assign this reference to a comments field on your list. If better parsing needed, might be difficult
2. Assign individual Flexi tasks and capture responses separaletly. We need it when we want to control based on output of each task. This would become complex workflow.
3. Go with single flexi task, This can be used if we want to save the comments on list item in a better way
   1. Enable versioning on the list and create a text field naming "Approver comments".
   2. Edit the flexi task form, use a hidden calculated value control
   3. For the above contorl , in formula field, set the task comments
   4. But, connect the control to our list column "Approver comments"
   5. Hide the contorl using a rule
   6. Every time a provides response to the tasks on an item, this sets the comments to our field. As we already enabled versioning, it displays one below other with respondent and time too. if we want the response along with comments, u can update the formula.

Hope this helps!

You can use another variable for Aprpover name, Similar to comments and in the form, use calcualted value and set the formula value to Current user. The current user in the form is the approver for that particular task.