Drupal is where its heading and what you should be looking at building your next site on. The reasons are simple. It is the most advanced cms today. Capable of more that Joomla and Wordpress. Although it needs a little extra work to get the features that come standard with other cms it is definitely becoming easier. Security an speed is also a major issue which Drupal wins on. So that being said it lags behind in a major area, and that is designers.
Drupal has far less themes than does most of the other content management systems. It also seems to cost more to get a designer to to a theme for you with Drupal. So you have a couple of options.
One is to make your own theme. They aren't all that difficult and with a little work you will have your own personal theme that no one else can claim.
The second option is to download artisteer, its a program that makes nice themes for you.. It is surprisingly effective and although it isn't free, the price is well worth it. It also has a fully functional free trial so you can test the waters.
The last option other than hiring someone or buying a ready made theme is to find a free one on the net. This is where Drupal is finally starting to catch up on. With a little research it is possible to find the theme that best fits your site, for a price you can afford, often times free.