Just wanted to add...from designing ships in SpaceEngineers (awesome fun, everyone should try it) an 8 sided triangular prism (look at a D8) is effectively the best shape for all round offense. You can always have 4 faces pointing at a target.

If you wanted to get super fancy you put a 4 sided triangular prism slap bang in the middle of each facing on the 8 sided prism, now you have facing in every direction. I designed a mega ship this way, I separated each facing by the width of the largest thruster available in SE this allowed positioning of multiple banks of thrusters in each of the primary 6 (up/down/left/right/forwards/backwards) directions without taking space from the flat planes, it was pretty **** awesome.