[CentOS] Piranha vs HAProxy vs Something else

I'm setting up a Apache cluster. All my web servers are on a private network. I would like to have 2 load balancers (1 connection to private network, 1 connection to the public network) setting in front of them directing traffic. They need to be session aware. My goal is to route all traffic through the load balancers and not allow anyone to directly hit the web servers.

I've looked at Piranha and am having trouble with the configs. I'm also looking at HAProxy/Heartbeat.

Does anyone have any success stories they can share and what type of load balancers they've used? All this needs to run on CentOS and be OpenSource.

Thanks, TR