Many have found happiness in either one of the alternatives. Some have found fulfillment with a single other person, others have found emotional satisfaction through a lifetime of one-night stands, or anonymous hook-ups.
But IMHE, neither is 100% realistic. I understand that even committed monogamists find it difficult not to stray, and a majority of them fall off the wagon at least once in their monogamous lives. Several friends who enjoyed a life filled almost exclusively of new partners, and have no regrets, found themselves drifting into the easy comfort and intimacy of a couple or throuple.
I know the question is hypothetical, and the two alternatives are extremes. But I still find it hard to reach an answer.