It depends on your flow, but tampons usually seem to work better if you have a moderate - heavy flow. Pads work well when you are having a light day, or are going to be less active (ex. Not running a marathon)
Depend a lot on what you will be doing that day too. If you're planning on swimming, or wearing tight clothing and doing gymnastic style stuff, tampons are pretty much an essential. Pads are totally convenient though too, so its purely whatever you just feel like reaching for when the time comes. Just do whatever, whenever.
Hi. My name is Elaine, I am an R.N. and one of the beinggirl.com women's health experts. I saw your question and thought I would also respond.
About whether to use pads or tampons, this is definitely a personal decision. The Always Ultra thin pads are so discrete and comfortable, you may want to try them. Tampax tampons give you the freedom and discretion to do whatever you'd like while you are menstruating, including swim. So you need to analyze your lifestyle and come up with the type of product be best for you. Your mom and BeingGirl.com can be a great help with this decision!