Hi Gus. “Better” is kind of a relative term I guess. I guess that you’re asking which will yield better results – true? My answer would be that as far as results go, it probably doesn’t matter much. If I assume that the workload is essentially the same with both methods, then the results should be essentially the same.
Where the “better” might come into play is in areas such as which would hold my/your/the client’s interest more, and thereby lead to greater exercise compliance. In that regard, my opinion would be circuit training. I love interval and circuit training for its variety and intensity.
I hope that this helps.