The products you list serve different purposes.
OPCode caches
There are many PHP Accelerators (OPCaches) as seen on this Wikipedia list. As is common with open source products, they are all fairly similar. XCache is the lighttp PHP accelerator, and is the default choice when you are running that HTTPd. It works well with Apache as well, however APC seems to be slightly more "plays well with others" socially speaking, being officially supported as part of PHP, and is released in-step with the official PHP distribution.
I abandoned usign eAccelerator due to its slowing development, and lagging against the releases of PHP, and the official blessed status APC offers with similar performance.
These products typically are drop in; no code change instant performance boost. With large codebases (Drupal, Wordpress) the performance can be up to 3x better while lowering response time and memory usage.
Data Caching
Memcache is a slightly different product -- you might think of it as a lightweight key value system that can be scaled to multiple servers. Software has to be enhanced to support Memcache, and it solves certain problems better than others. If you had a list of realtime stock values on your website, you might use Memcache to keep a resident list of the current value that is displayed accross your website. You might use it to store session data for short term reuse. You wouldn't use it for other things such as full-page caches, or as a replacement for MySQL.
There are also Wordpress addons such as WP-Super-Cache that can drastically improve Wordpress' performance (infact, WP-Super-Cache can rival static HTML based sites in many cases)
In summary -- I would highly recommend APC if you want a "set it and forget it, well supported product".
After more research it seems like another (possibly better way) to answer this would be to setup the www folder like so.
sudo usermod -a -G developer user1 (add each user to developer group)sudo chgrp -R developer /var/www/site.com/ so that developers can work in theresudo chmod -R 2774 /var/www/site.com/ so that only developers can create/edit files (other/world can read)sudo chgrp -R www-data /var/www/site.com/uploads so that www-data (apache/nginx) can create uploads.
Since git runs as whatever user is calling it, then as long as the user is in the "developer" group they should be able to create folders, edit PHP files, and manage the git repository.
Note: In step (3): '2' in 2774 means to 'set Group ID' for the directory. This causes new files and sub directories created within it to inherit the group ID of the parent directory (instead of the primary group of the user) Reference: http://en.wikipedia.org/wiki/Setuid#setuid_and_setgid_on_directories
Best Answer
Those files are cached adds to be served. Don't worry if number of files is greated than the number of unique banners you have ever served - multiple files per banner are common.
You can delete the files as often as you like (even every 10 minutes if you feel like it :P) - if you do it too often the only penalty is slight performance decrease - if they are still needed the file will be generated when add is first served.