I will start this post by saying that I have used Apache for more than 2 years in production environments and I am quite experienced at optimizing Apache to accomplish the goal at hand should it be handling thousands of connections simultaneously to serving dynamic web sites quickly and efficiently while minimizing the memory footprint.
I have in the past fought tooth-and-nail for Apache’s ability to match LiteSpeed Web Server’s speed when serving web sites. Apache can be configured to be nearly as fast if not just as fast as LiteSpeed but the problem is that Apache requires in my own personal testing nearly two times as much memory and FastCGI to come close to LiteSpeed comes out of the box. LiteSpeed claims to serve static content up to 9 times faster than Apache and PHP up to 50% faster. While I won’t go into depth as to which one can do what faster, I will go into why I chose to move my company from Apache to LiteSpeed and what benefits we have seen. If you want to see benchmarks that compare LiteSpeed and Apache I recommend you search Google.
My company has relied upon Apache for years however I recently began testing the latest version of LiteSpeed which has come a long way. LiteSpeed out of the box offers the performance of an extremely-optimized Apache installation with half or less memory consumption in my testing which is a major benefit. Apache is very weak against certain DoS attacks such as a HTTP Request DoS which doesn’t require a large amount of outgoing bandwidth but can be devastating to an Apache web server where as LightSpeed takes such attacks in stride in my testing.
I found personally that the overall “feel” of browsing various test sites, both dynamic and static, felt snappier or zippier which is an additional benefit to running LiteSpeed. In the end if you know what you are doing and you have the RAM in your server to accomplish it you can match LightSpeed Web Server’s speed at the cost of efficiency.
LiteSpeed’s Web Server is a direct replacement for Apache and installation was a breeze. LiteSpeed supports all of the popular control panels and all of the features of Apache except for your old Server Side Includes but who uses those any more? In my experience on a cPanel based web server you can log into WHM and switch between LiteSpeed and Apache at any time and you can run LiteSpeed on an alternate port for testing any sites that you wish to make sure will function correctly before “making the switch.” I have yet to run into any issues that are caused by LiteSpeed however I will post an update if I do run into any.
At the end of the day my advice is to spend the extra money you would be paying to add additional RAM into your server on a LiteSpeed Web Server license.
Edit: LiteSpeed 4.0 *does* support Server Side Includes even though the current FAQ on LiteSpeedTech.com says that it does not.