The Only DIFFERENCE: in Uta no prince you don't have the fantastic touch, the heroine have real skill, and not a fairy behind her. It's OBLIGED you like one, you will like the other. They are actually very similar, uto no prince sama is basicly a bording school of music, composing and singing, where a girl comes to the school, and there a a few boys with differnt personalities, that all admire her!
Then there is kiniro no corda a bording school of again music but this time focusing on intrumetal music. And a girl again is surronded by boys, and helping her! Kiniro has a twist of magic though! But if you like one you probily you would like the other! Oh and i LOVE both of the sound tracks, also they have pretty good art! Both female protagonists must learn some form of music (violin and composing) with little or no former experience.