Well I spent loads of time fixing the short falls of Joomla and it's SEO, just read their own forums and see how everyone wants better SEO for it. I do agree that it is a very good CMS, if not for that issue, I use it on 5 sites myself. But as far as a CMS, what do you plan to do, that has a lot to do with the choice IMHO....
I bet my SEO Website CMS can beat it with its numerous built in SEO tools For example the thing that I'm most proud of is the BOT Trapper and and Search Engine Keyword Tracker , not to mention the Link Exchange Directory Module which is handled on Subdomain in order to preserve the quality of the primary page. They will be included in the BETA version which hopefully will be released next week. Cheers, Venetsian.
Joomla! obviously... someone said there were alot of add-ons and extensions for another CMS? There are 1600 third party extensions for Joomla! of which 90% of them are free... it takes 2 seconds to add a sitemap, and it uses modern web design standards, which makes SEO much easier I bet
Joomla is a good CMS that you can optimize well.... I'm sure there are a many others, but I know Joomla for sure can be optimized well.
I think Wordpress is one of the best SEO-friendly CMS's out there -- especially with a few of the necessary SEO plugins.
The Joomla mod I'm referring to is Artio JoomSEF for better SEF management with Joomla! It may require a small rewrite of the htaccess file to work correctly. I don't know what SEF for Joomla you're speaking of that costs money, there is a built in one that is free, and Artio is also free. While there are many commercial (read paid) addons for Joomla, the vast majority of the mods and components are free.
One vote from me also for drupal. The themes are not that great but if you can live with that then it's very SEO friendly.
Drupal - Hands down Drupal that has gotten me in the Google top-5 for many competitive keywords (not my non-existant SEO skills) ..