Just use it. It is undeniably the best CMS out there.
I could easily deny this. A thorough understanding of a more powerful CMS such as Joomla and WordPress looks like a fluffy little baby bunny rabbit with the cutest little button nose you ever seen.
Joomla is far more versatile, can WordPress be adapted to do
half of what Joomla is built to do? Perhaps. My lawnmower has wheels and drives, but I don't take it to work in the morning.. Even though I could duct tape a windshield and doors on it.
Joomla is far more secure. If you don't keep an eye on your WordPress site, it can get spammed to death, malicious injections (bad, bad, bad!! Imagine you're in the SERPs getting clicks and one day Google labels your site as malicious.) I just went through this with a bunch of WP installs and the timthumb exploit.
Joomla is more stable. I have heard some bad things about WordPress in high traffic environments. Bottom line is, WordPress is a blog. Not a CMS. Yet.
Don't get me wrong, WP is awesome and I use it every chance I get. Setup is a snap, templates are very nice, lots of extensions and modifications are easy. SEO is out of the box... Pretty good; getting rid of the category base is important for fixing it's out of the box URL structure. If you're planning to blog, I would also recommend fixing it's "Next/Prev" post links so that instead of them being titled "Next Post," they use the title of the post they link to.
Both of these issues are cleared up with plugins in a matter of minutes, but big deals IMO.
Joomla is far more powerful, though. SEO takes a bit more to setup and it's not user friendly like WordPress. If you haven't been using Joomla for years, don't plan on making anything good with it; but if you have, it canNOT be f-ed with. WP isn't even a close comparison. Not even distant. Not in the same league.