Reading contact lenses: one of my eys has l:0.00/-0.5x55. my optician suggested going with 0.00/-0.75x55 contacts, but they were not sure. some people on the internet said to divide it by 2 and make it -0.25/0.00x55. which option likely to be better?

These numbers are very low. Do you really need to correct these eyes at all. At your age you should be able to see at distance and near practically everything without the need for contacts or glasses.

Mild myopic astigmatism in one eye only is not usually a big problem except while night driving. Try starting with a clear pair of eyeglasses for driving and other far distance tasks. If the right eye has little or no refractive error, the risk of contact lens use is probably greater than the benefit, while eyeglasses are practically no risk at all.