I can only share the value and atmosphere of each of these two places as I have felt and The Mother herself has indicated.
The Ashram contains a very special personal atmosphere of Sri Aurobindo and The Mother. The Samadhi is especially charged with Their personal presence. The Ashram is an intense place, an advantage if one wants to sincerely pursue the true spiritual life. But because of the intensity of action of the supramental force here, it also brings out many defects and insincerities hidden within us.
Auroville is different, a wide and experimental township meant to primarily realise the Ideal of human unity through an evolving humanity engaged primarily in the karma yoga in the true sense. Unlike the Ashram, Auroville is much more impersonal. Karma and gyana are the prominent notes here, unlike the Ashram where bhakti, faith, devotion are much more valued.
Of course, a sincere individual can engage in the sadhana and realise its truths anywhere. The Ashram and Auroville can provide the needed atmosphere. But someone who is insincere remains the same wherever he lives.
Rest one has to decide based on the highest aspiration within oneself.
Hope this answers your query to reasonable satisfaction. For the rest, one has to come and try for oneself.
Affectionately,
Alok Da
