1. When a new bot is added, always use that bot first. This assumes that the user added it intentionally despite already having bots for that function.
2. If bots are ranked too closely, pick one at random.
3. If bots are ranked too closely, ask the user which to use. Have an option for setting that as default. If you have an Android phone this should feel familiar. This is how Android handles different apps that handle the same function (i.e. what app should open when you click the mailto link).