My own experience has taught me that because everybody's different and everybody wants something different there are no absolutes. To complicate matters, the body quickly adapts to whatever you're doing so you may get great results with a 3-day split for a few months then, suddenly, nothing... You never had any luck with full body workouts or circuit but then you reintroduce one or both and, voila, results are happening again... for now. Most of us aren't scientists so, though there are scientific reasons for why we are or are not getting results, It always seems to feel like anything you do is a crapshoot. Everyone knows more muscle = more fat burn but when I did nothing but weight training and stopped seeing results i re-instituted cardio in the form of HIIT on the treadmill (CardioCoach) and started seeing results again. Then I brought back my old FIRM circuit routines (which had given me great results once, but then didn't) my results really picked up steam. My workout history has taught me those results will eventually cease and I'll have to change it up again. In the end, I've found you need to keep changing things up and play around with different types of physical activity to keep the ball rolling. I read everything (particularly over at FigureAthlete.com, especially Chad Waterbury's stuff) but it's best to take everything with a grain of salt since even the "experts" don't agree. If you've gotten great results doing plenty of cardio you can change up what you do but why give that up if it works? If all the cardio in the world isn't getting you what you want you should turn to weight training (comes in lots of forms). Like Arnold said "Do what works." I'd add, until it doesn't. Then your body's telling you it's time to try something else.
One absolute, though. Like someone here once said "You can't work out a bad diet." True for everyone.
