Most Helpful Girl
i also have medium brown hair & have tried both ways. this has been my experience (if it helps):
highlights look more unnatural, and fade greatly within a month. the highlights turn brassy, bright yellow soon, & there is a lot of "up keep." it also damages your hair greatly!
i've also tried a solid darker color all around, & med brown + black low lights. my skin tone is pretty light, so the darker, solid color didn't look good at all. the black lowlights were hard to see & blended too well. that wasn't worth it.
right now my hair is it's natural color. & I may do black low lights to add more dimension, but I'll never do blondish highlights again..it was really difficult to grow my natural hair color back :(
have fun & good luck! (: