I selected Warden for a couple of reasons. First I like druids. Second, I did not want to turn into a lion because I like wolves better. When I started out I did not know how effective the character would be, but as I have played him to level 20 I absolutely love the character. Druids/Wardens are amazingly effective due to their HoT. I have been in many groups where the HoT is our only saving grace ticking away while other spells are recharging. Because of the HoT we do stack well with Reactive Heals or Wards.
Warden can certainly be the main healer but if there are two healers it is sometimes better to be the secondary healer and be able to contribute a small amount to the DPS.
In the end I think all of the healer classes are good. It is just a matter of how you enjoy playing the game.