I prefer rules-heavy, although I see why people call 3E "rules-light" or "medium", since far more complex systems such as Champions or Rolemaster exist.
I classify 3E as rules-heavy, and I like it that way. It gives the players something to work with, and a foundation to stand on in the greater context of the game.
A non-rpg friend that I described DnD to one time (days of 2nd Edition) responded with "That sounds really arbitrary." I winced. I've always tried to find ways to make the game as non-arbitrary as possible, as I feel it creates a more enjoyable experience.
Just my two cents.