Joomla vs. WordPress
If you are a little more technical and bent up on where exactly things are placed on your website I'd go with Joomla.
Joomla runs on modules and depending on what template you picked you can have 30 of them in different places on the site. You may want a calendar on the front page in module one, but on the form page you may want an ad or a picture. Joomla makes it very easy to place objects where you want them and on which pages you want them. The other cool thing is that each article already comes with a place to put meta tags and descriptions.
There are about 30,000 + modules and components that you can use with Joomla. What I have found is that some of Joomla scripting can be loose and some modules and components can conflict with others. Most of the time it's and easy fix. If it's not try finding a similar component are module. After installing any new code on Joomla, go back through the site and make sure everything functions normally.
Unlike WordPress, Joomla will let you install new code that conflicts with the rest of the site and you'll get some very scary .php code running at the top of your page that will trip you out. However if you just uninstall the module/component/plugin then all will return to normal.
WordPress is the newest craze to hit the web, it's a blog first and a website later. WordPress dosent give you as many options to place things where you want as easily as Joomla however you can you can pretty do as much as you can with WordPress as you can with Joomla. WordPress runs on plugins and widgets. The cool thing about WordPress is that you can find and load widgets from within the install. It also will disable a widget if it tries to take down your site.
One of the best features is that it is extremely easy to use. I would suggest getting a self hosted WordPress site, installing it at WordPress.com limits your functionality significantly. WordPress also has 30,000+ plugins. I have that found WordPress is just not as robust as Joomla, but most people don't need robust, they need easy and quick. If that's you then go with WordPress. If you creating a league type of site that's going to have a bunch of stats and schedules, team and member profiles then I would go with Joomla.
I have reached top rankings with both Joomla and WordPress, and have used both for e commerce. So it's really going to depend on your individual needs and your learning curve. If you have the time and the knowledge I would go with Joomla first. Going from Joomla to WordPress is a breeze, but going from WordPress to joomla is like climbing a mountain. Way more code with Joomla and sometimes the site doesn't look as expected if you do not use all of the modules that the template used often leaving gaps on the screen.