Which Apache2 server should I use?

[Damien Hull]

I'm setting up a few test web servers running Ubuntu 10.04. I installed a LAMP stack with "aptitude install apache2 mysql-server php5 php5-mysql". It looks like I got apache2-mpm-prefork. Is this the version of Apache I want? 

I also need to performance tune it for 256mb of RAM. That's all I have unless I migrate to a larger server. Any tips in this area would be a big help.   

For those that don't know there are two kinds of Apache2. 
apache2-mpm-worker
apache2-mpm-prefork