Difficult question, they are all good for different reasons and I don't know you taste which would be helpful but this would be my choice:
Wuthering Heights--is considered one of the best classic romance novels ever written albeit a bit on the dark side and in the end everyone gets what they deserve.
http://www.sparknotes.com/lit/wuthering/…
Farewell to Arms--Also a love story of a very different type but the allure of this book is if you haven't read Hemmingway you really should. He write mostly short declarative sentence but they are so powerful you will not want to put the book down.
http://www.sparknotes.com/lit/farewell/s…
Jane Eyre--is a gothic romance novel that showcases such themes as:
Love versus Autonomy
Religion
Social Class
Gender Relations
http://www.sparknotes.com/lit/janeeyre/t…
Really, you can't go wrong with any of the choices and if you run into trouble I think all of them are on www.sparknotes.com to help you out with understanding anything about the plot or things like that.
Stated in the text of the answer.