Third year in a row Valencia is the No.1 RB for me in FIFA 19 EPL. He is fast, strong and with excellent standing tackle. He backs into players and he is able to get the job done! Dont waste your coins on Walker. This guy can clear the ball just as easily and this year he can get some headers for you too. His pace in this new fifa feels great, his passing is really good and his balance is decent.
Those two seems to be the only weaknesses in his game. He doesn't miss much but when he does miss a header due to his height/ jumping is noticeable.
In FIFA 18, he was definitely the best RB in FIFA. But this year he does not feel so good. He seems weaker, his tackles are not so good and he does not go in attack often. His pace feels very good and he can catch anyone and his passing and crossing is very good, too. To sumarise, I think that he is the second the best RB after Walker, but Kyle's price is very high at the moment. So buy Valencia for now and when Walker's price drop, buy him.