Hi there, thanks for your query.
Milford Sound is one of the places that can be enhanced by the rain. Rainfall tends to create a series of temporary waterfalls. For this reason, waterfalls are one of the highlights of both your trip to Milford Sound.
Weather aside, this link here will show you a list of operators that advertise with us. Most will have booking calendars that can you guage how busy they might be. Due to having advertisers pay to list on our site, we're unable to promote one over the other, hence directing you to the above link.