We drove from Te Anau to Milford Sound and it was an easy drive, but it was breathtaking! Driving yourself you get to stop along the way and see the different areas, walk around, and take pictures.

Don't know how the weather will be. I don't think there could be any minuses. It was raining a little when we went in April and the waterfalls were spectacular. I recommend booking through Mitre Peak Tours. They are a smaller company with a smaller but very clean boat. They were the only tour that went beyond the channel into the ocean and their price was best. We did not have a boatload of tourist which made it very enjoyable.

I booked in advance online thru the central office - I think there was a discount but check.

Smallest boat - Mitre Peak - gets you right up to the seals and almost under the waterfall. Great crew. Also the price varies by the time of the day. The afternoon cruises after 3 pm are cheaper. But winter time gets dark earlier too! You can book when you get there. Discount sites like bookme sell you the tickets to the same boats for less but generally these sell out a few days in advance