Cooking the rice in water is healthier and produces tastier results because all of the rice nutrients and flavor are preserved. Whether in a rice cooker or a pot on the stove, the trick is to have the right ratio of water to rice, generally 2 measure of water to 1 measure of rice, plus salt to taste. The rice cooks in the water and absorbs all of it, except the small amount that escapes as steam. The result is fluffy rice that tastes like rice.
Steaming, OTOH, extracts some of the few nutrients there are in white rice, which ends up in the water that goes down the drain along with a lot of the rice flavor.
Rice is easy to cook without a rice cooker. Put one cup of water and 1/2 cup of rice in a small non-stick pot, cover, and bring to boil over high heat. Reduce the heat to a simmer. For white rice, simmer 15 minutes; for brown rice, simmer 30 minutes; then remove from heat and let the rice sit, unopened and undisturbed, for the same amount of time (i.e., 15 minutes for white, 30 for brown). Fluff with a fork and serve.