It's waaay too early to decide on this yet. We have no idea how different the two versions are going to be, and even though most pairs only differ on very insignificant levels, I feel like games covering the topic of environmental change might offer a bit more towards the differences between the versions than what is usually done. If it means that one version is gonna take place primarily on water, then I'll be sure to get the opposite version. Right now I'm definitely leaning mostly towards Omega Ruby though, since Ruby was the first version I ever got and played.