Queen Rania (who's on the poll, but who isn't really a princess): I like what she's doing by bringing education to the forefront. From what I can tell, she's knowledgeable and articulate about issues she's interested in.
Princess Maxima: Same as above, except she's interested in Microfinance. Talks intelligibly about it.
Princess Mette Marit: her simplicity is something I've always liked. The fact that even though she isn't knowledgeable about issues as the above (due to her background), she's willing to learn and from what I can tell, she has a very warm personality.