I find it's almost always best to open with a Ruby. After that, it depends on KD strat. As was mentioned earlier in this topic, picking Ruby is never a bad decision. It isn't always the best, but is never the worst. The other dragons can have their uses but are fairly specific.

Since you did mention it is a ghetto, sending a Ruby will most likely give you the best results, followed with a Ruby replacement if you can get the support for it/if they manage to kill the first one. If you end up in a knock-down, drag out war where neither side gives up or agrees to mutual peace then try Ruby - Ruby - Emerald or Ruby - Emerald if they take 3-4+ RL days to kill the first one so you can show a numerical advantage in combat gains and give them a different set of reasons to contemplate ending the war.