It mainly has to do with the time you have available. If you have time, diversifying is good, it's more fun. But it means you need to train more than once a week. Training in various disciplines has the risk of making you lose your focus. Try to find a rhythm which suits you.
I would say that shifting sports is excellent... It mainly depends on your motivation. If I had time, I would practice 3 or 4 different sports myself. If you opt for 2 trainings a week, my advice is to combine for instance aerobics and fitness, or tae bo and power training.
Changing rhythm, schedule or program ads fun as well and keeps your training alive.
-------------------------------------------------------------
Extract from a short interview with Haaije Pijl