The more I use the defender, the more I really like it. That being said however.... The only list I've flown with two of them in it that actually felt like it was competitive in a tournament setting was two PS3 defenders and a recon spec bounty hunter. Simple, but effective, and actually pretty fun to fly. For fun the double defender HLC and Jonus can be really good, or really bad depending on if your dice like you or not (mine generally don't).
Used this myself several times it's a meat grinder with few weaknesses you can easily be attacking each turn and it's tanky, double focus on firespray works so well.