The books can be easily read standalone, there is very little cross over between them (despite having the same protagonist). If you read them in publishing order (which is also chronological) you will get a little more from it.
However, the three books have quite different appeals. Beyond the common theme of symbology:
- Angels & Demons (my favourite) combines technology and religion
- The Da Vinci Code has a lot about puzzles and history
- The Lost Symbol is Freemasonry, and has more "action" than the last two
Given that the crossover is minimal, this could influence any choice in reading order (or even whether you read them all!)