May I suggest a strawpoll? (https://strawpoll.com/) Most people feel more comfortable "voting" for these matters when they're anonymous ;)
Personally I think mergig isn't a bad idea, but don't delete the community that ends up not being the main one. Rather post a sticky then like "we moved to XYZ" and ask for future content to be posted in the other community. That way, people looking for the keyword "bunny" will end up in the rabbit community or vice versa and you both get more traffic / subscribers.