Hmmmm....this is tough one. I would have to say LOTR as a trilogy (including the Hobbit) beacuse they were the first books i read out of the series and is very intereesting etc and all the other reasons why we fans love it soooooo much. But then the Silmarillion was also excellent beacuse it told the history of ME and was v. interesting to read (but with hardly any dialogue it made it harder to understand.)
Therefore, im going to have to say LOTR and Simarillion😄
All the other books in the series, including the lays of Beleriand and The Shaping of ME, are also excellent and thats why i dont like choosing between things because to me they are all great and i love them to bits😄