Joomla SEF Components
There are several SEF components for Joomla; such as ACESEF, sh404SEF and SEF Advance. Using SEF components will rewrite URLs and provide a nice, clean look in the browser bar. Using Joomla’s built-in SEF urls with .htaccess works fine in many scenarios too.
Commercial SEF Components
Many extensions work well, especially if they are up to date. Some come with nice features like flood protection and url naming for specific extensions. They are excellent products. However, issues could arise when some extensions and components (no matter which ones) are mixed with each other. For example, it could make great urls in a forum one day, then using an upgrade fropm the same forum could make SEF urls uglier than the built-in Joomla SEF. Upgrading is where things can go haywire. Issues can arise if PHP is upgraded on the server and the extension was created prior to the upgrade. Furthermore, as some companies evolve, so does the pricing. Some may want a yearly license, etc.
The extensions can do do an excellent job and offer excellent control for which to name the URLs. But, well written articles, appropriate content and good link management should still have priority over how a string is displayed in the address bar.
Joomla Built-in SEF
Using SEF urls with Joomla does make a more professional look. Using the built-in SEF is free and can be set in the global configuration. Renaming the htaccess.txt to .htaccess will allow you to make custom urls. Personally, sef urls are something I would always have on a Joomla website. Since a good home page, link structure, page titles and excellent related content does more for SEO and nobody really cares about what they read in the address bar, using sef is the icing on the cake…. completing a professional look rather than some weird looking string.