There's this one girl at my gym - she has that sort of solid fat look - you know - big girl, clearly overweight, but she still looks pretty and cute - it kinda suits her.
Anyway - for a year now, I've watched her practically kill herself on the stupid circuit, every time I'm there, she's doing the circuit - she's obviously quite fit from it, but damn, her body shape hasn't changed a single ounce. In the meantime I've put 30kgs on my squat, 35kgs on my dead, and 5 kgs of mass on my body - not all muscle of course, but I've put on mass in the right places.
Circuit isn't a terrible thing if you push hard at increasing your weights - but most people don't have a clue and just do the same weights every week, and look the same every year.