IMHO, my answer would have to be neither of the given options. I'd say the very small
group lessons are the most conducive to effective learning.
On average, the Aikijutsu Dojo
where I study will have 4 - 6 students [includes two black belt students] in any given class. This small number of students affords a lot of individual attention can be given by the head sensi during the 2.5 hour class.
BTW, this is my first post on AikiWeb Aikido Forums.