Let me pick up this old thread again, recently LordHavoc has revised the havoc mode and made some very nice improvements.
Especially the rocket launcher with guided rockets works much nicer than in stock nexuiz. I would love to see the havoc RL taken over for the default mode, mainly because it allows for a faster gameplay.
Guiding rockets at their current speed (850) is very time consuming, and you are forced to stand still for quite a while to do proper aiming. This makes you an easy target, and does not encourage faster gameplay. Also you're not going to catch a flagcarrier with it when he's laserjumping away quickly.
Havoc RL is much faster (2200), but also harder to control due to it's speed. This makes it more useful in many situations, but very hard to control (you will rarily get direct hits if your target is moving). Also it is much nicer to twist rockets around curves.