It depends -- I would actually suggest trying the diva cup (google it) -- it's kind of like a diaphram, works really well, is environmentally friendly, and good for your cootchie.
Tampons are *ok*... Like most things we use in our society, they are chalk-full of chemicals!! Unbleached tampons are best (you can buy them at health food stores), cuz if you think long and hard about it, you probably don't want to have a bleached wad of cotton shoved up your vag. Use the *smallest* tampon possible -- don't use a super-size when all you need is a regular. If your flow is too little for the absorbancy rating, the tampon will leech the important natural moisture your vag needs to keep itself in working order.
Like everything, there are small inherent risks like toxic shock syndrome -- but it's rare and if you use tampons wisely (like following all the rules on the instructions), you should be fine.