You better get both, put em both on layaway, beleive me from a Woman, you will be in big trouble, that guitar will be her worst enemy so buy both, a Womans mind is wayyyyyyyy different from a Mans and she will somehow someway someday make you regret the day you got the guitar and not the ring....
Make your girl in her material ways happy as you can then you can play your heart out on your new toy.