I've spent quite a bit of time playing with site optimisation tools and plugins, from Cloudflare and WP Minify etc. I normally use WP SuperCache but I have tried W3TC on a number of occasions, and each time I end up deactivating it.
One of the problems at the moment is that the Cloudflare part does not seem to be working, it keeps saying it cannot connect the API (and yes, I've been through the work-arounds and checked that I put in my domain correctly). I have been reading a few support threads on this issue and there doesn't seem to be a work-around.
The other thing that annoyed me are the contast messages that appear in the panel. The main issue, however, is that after installing this plugin my site speed tests had me dropping a couple of %!
In the end I reinstalled WP Super Cache and the official Cloudflare plugin.