I'm not an expert with any of them (and haven't used Joomla at all) but it depends on what you want to use it for. Wordpress is good for blogs, article sites, stuff that has a lot of content served dynamically but doesn't require too many add-ons or e-commerce. Thats just my opinion - others will argue.
Drupal has a massive amount of plug-ins and modules, there's nothing you can't do. It is incredibly extensible but that can also be a curse. It is great for e-commerce and functionality similar to that but is almost always overkill for sites that are merely dynamic in nature and don't need specialized modules.
Just try updating it when you have extra modules added and you'll see what I mean.
Anyway, I hope that helps.
Joomla was voted as the best CMS over the other last year by a panel of web developers in the so-and-so conference, and you can use it because it's very easy to set it up and go about it - more than th others, except WordPress maybe, but that's for blogs, articles, and similar stuff.
As previously suggested..it depends on what you are going for. I personally tend to lean towards E107 because I found that I can best control the layout/design. Some CMS's have template systems which leave many of the sites that use it as a back-end look similar. I can surf the 'Net and sometimes know what they're using by how the site looks.
I do not know if you have a server host but if you do and they offer CPanel or similar control panel they often have a one-click installer which will set up the database(s) and necessary files needed to run the CMS. It would allow you to easily/quickly fully test them. And if there's something about it that you don't like or you decide that it will not suit your purposes there's also usually a one-click uninstaller to remove it from your system and will drop the associates databases.
Hi, i am going to have to say that http://www.concrete5.org/ is by far the best and most user friendly CMS. Really nice and opensource. Its not as comprehensive as Joomla or Durpal but its really nice for small business or small sites.
But as to answer which is the best CMS, I think it would depend on the needs of your clients and your skills as a web developer. But for ordinary blogging, I will vote for Wordpress because it's easy to use and SEO-friendly.