I prefer them together, usually circuit style. If I do weights alone, I don't feel like I've gotten a good workout in. However, I also KNOW that my body needs at LEAST 4 days with 30 minutes of cardio each week to maintain. I've learned that by trial and error, so I stick to that format in some way.
I also include leg weight workouts as cardio days, since they send my heartrate soaring.
My 5th day is a freebie, whatever I feel like doing or want to hit harder that week.
you know I if I work out really hard its almost impossible to lose fat. It seems like I cant control my diet or my body doesnt want to give the fat up or something. So now I am only working out 3 or 4 days a week and tightening up my diet. Lets see what happens.