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Plugins are one of the main of the strengths of the WordPress system, allowing non-technical users to easily extend WordPress capabilities. In fact, coupled with custom theme development (more on that later), it’s easier than ever to build your WordPress website exactly how you want it!

But which plugins are worth using?

That’s a really good question, and the answer is… “it depends.”

What the plugin does is only part of the story. A good plugin will give you leverage, and won’t leave you stranded when the plugin author abandons the plugin’s development.

Here’s some guidelines for choosing plugins:

• When was the plugin last updated? Really old plugins may not work in the latest versions of WordPress, so check the date carefully. If you are using the administrative web interface for plugins (“Plugins >> Add new”), WordPress will tell you how many days since the plugin was last updated.
• How experienced is the author of the plugin? Is the author a full time WordPress or web developer, or part time hobbyist? This may or may not matter, but it’s good to know. Hobbyists have more time to devote on single projects, until they get tired of the project. Professional developers may have a pretty long lead time for fixing bugs (or not), but may have long term plans for supporting plugins far into the future. Check the plugin home page to get some insight on the plugin author. If the plugin home page hasn’t been updated in a year or two… that’s not an encouraging sign! If the plugin home page has been recently updated, and has attracted a lot of comments, that’s a pretty good sign.
• Is the plugin critical for your design? Be careful in trusting critical elements of your design to components outside the WordPress core. This can be very painful when the plugin is does exactly what you want… except for a showstopper bug. That pain is even worse when the the plugin code is too complex for casual bug hunting. (I have a particular plugin in mind… it’s even installed on this blog… I just don’t use it. I’ve donated money to the author, I’ve sent him a screenshot along with description of the bug, but he has no interest in fixing it. So I don’t use it, and I won’t recommend it.)
• How highly is the plugin rated, and by how many people? Ratings run from one to five stars. Typically, a 5 star plugin has exactly one rating. The average rating for common, useful plugins is about 3.5 stars, and that’s about right. More information on ratings can be found on the WordPress plugin web page.
• Has the plugin been tested against your current release of WordPress. It’s usually not too difficult to test a plugin against any release of WordPress, and if a plugin is months out of date against the latest version of WordPress (which itself may be months old), be careful!
• Is the plugin listed at WordPress.org? There are a couple of plugins I do NOT recommend here at WIAW because the plugins authors can’t or won’t list them at wordpress.org, and require you to follow their websites for updates, possibly requiring blunder-prone manual updating as well. Note that most of these types of plugins are otherwise fine, but using them will increase your maintenance requirements.
• Compare different “Top Plugin” lists. Do your research for plugins to find other articles listing top plugins. Print out several of these articles and compare the lists to find the plugins everyone agrees are best. Use those.

WordPress.org hosted plugins

I typically stay with plugins distributed by WordPress.org, for several reasons:

1. The wordpress.org plugins are hosted in a public plugin directory. There is very low risk of installing malware plugins. As a counter-example, a business partner and I installed a 3rd party (not from wordpress.org) plugin to handle mailing lists. The plugin author had a remote procedure call to the plugin authors home page, where the plugin was supposed to “check in” during installation. As it turned out, the file on the author’s web site was broken, so the plugin would not install. Probably a good thing for us!
2. The second reason is that being hhosted at wordpress.org gets the plugin listed in the “Add New” page. So anyone writing a plugin hosted at wordpress.org gets included in search term results. This makes it easy to find plugins, wordpress.org does some of your promotion for you.
3. Updating plugins hosted at wordpress.org is easy, the process is largely automated with most of what little required work is necessary being done by the plugin developer. All you have to do is check for updates through the administrative interface, and update as necessary.
4. All the plugins hosted on wordpress.org are General Public License, so you are free modify them, learn from them, and use them as you will. Use an existing plugin to make a new plugin. Then post your new plugins on wordpress.org and watch your website traffic go up!

For a different perspective, check out these guidelines used for judging the 2009 WordPress plugin contest.