Circuits are generally for fat loss, light weight and higher repitions done back to back, or a number of exercises for a "round" so to speak.
One thing that is a mixture is supersets, for example a chest and back super set would be pull ups and then push ups, or DB press followed by DB rows.
As far as what is best for muscle, standard way. Supersets however are great for people who have been doing the same thing for awhile, and need a new shock. You will certainly build muscle doing supersets, some do them all the time, some only every now and then.
Moving the workout to saturday will be fine I imagine, plenty of rest.
Circuits are generally and originally designed for sports performance, not fat loss.
