Stats from their official forums (Today 18 May 2009) #1. http://forum.joomla.org Total Posts 1,633,712 #2. http://wordpress.org/support/ Total Posts 1,041,031 #3. http://drupal.org/forum Total Posts 642,516 Joomla's The Best
Just because joomla has more post in their forum, does not make it the best. In fact, I think it means just the opposite. The number of post show that people who use joomla need more help then people that use drupal and wordpress. Its called a "support" forum for a reason, because people go there for help. If something was easy to use and secure, you will not need too much help. So you want to look for a popular CMS, where few people are asking for help. That is going to be Drupal. Its kinda like a car. Do you want to buy a car that breaks down a lot and you need help, or do you want to buy a car that is almost maintenance free? All of those post in the joomla forum are there for a reason. And its because joomla breaks down a lot.
Joomla has so many more plugins than drupal, and if you look in the Joomla forum you will see all of the different threads. That is why the number is greater, besides popularity.
I like all of them, find wordpress the easiest but it lacks some of the others ability. Joomla seems to me to be more complicated but, I don't use it like I use the others. Drupal I use on most my sites now. I typically get a free drupal templates their or with a drupal search (the above doesn't require link backs.) Again Joomla and Drupal should be used if you want to expand your site heavily. Which one you choose is your choice, I actually would like the joomla fans to try to persuade me to switch as I haven't done a ton with it and would love to hear their comments.
Drupal is the best,but it's not easy..We have to undestand about program.. joomla and wordpress is easy..and many use it. I used wordpress in my website.
A lot of the plugins that are listed on the joomla site have known security issues. Popularity does not make joomla more secure or better the drupal or wordpress. When you get down to the details, there is no reason for joomla to be popular. Except that misery loves company.
if Joomla the best why I never see popular huge sites with high traffics or big companies using Joomla the one and only I know is Porsche Brazil and it doesn't use joomla anymore for Drupal you can see the list at Dries Buytaert personal site
wp is great, but joomla is sooo flexible and there's a zillion components/modules for joomla(that can also make a zillion security issues )