I have no clue as to what is the best month, but I can tell you that I was there in mid July of this year. We lucked into a week with no rain, which is unusual. The reason we chose mid July was that we wanted to be there during the salmon runs. The salmon draws out the bears and the eagles. If you like wildlife, it was a great time to see it. Buy some books on Alaska and read up on it. They may also help you make a decision. Good Luck and have a Great Trip!!
We went in mid-May -- first cruise of the season. Alaskans told us that while the temperature is cooler...in the 50s typically...this is the best weather. We had one short shower while in Ketchikan...that's all in a total of 12 days.
We missed the summer flowers but we saw lots of snow on the mountains. We also missed the salmon running, but there was no shortage of delicious salmon.
Whales have just returned from Hawaii in May and are actively feeding. Other wildlife is coming out of hiberation. In addition to whales out our dining room window, we saw sea otters, sheep, and moose.
I really like mid to late August. For the snowy mountains May is tops but wildlife is not as plentiful and Denali shuttles do not start until June. It is also NOT common to see sheep and moose from your ship- this is unusual. Most any wildlife viewing must be done from an organized tour. I always whale watch from the front of the ship but few passengers are willing to invest the considerable amount of time this requires. This is based on 10 Alaska trips. Forget going in Sept- salmon runs over, very unpredictable weather that gets worse as the month goes on, Denali shuttles close mid Sept. dark by 7pm.
We just got back last week, we went Southbound the first week of September. We saw moose, bear, whales ottters and seals, and hundreds of bald eagles. Yes it rained some but from what we were told that can happen anytime. It got dark at 8:00 pm just when it was time for us to go to late seating dinner. We saw snow on mountains maybe not as much as one would see in May. I think whenever you choose to go is the best time.
Just got back, went the first week of Sept and had only one day of rain, and that was in Juneau. We were told there to come back in Late May or June because that is their summer. The flowers were beautiful, saw eagles, whales, sea lions,
and the salmon were running, we thought it was wonderful!!
We went on Dawn Princess 6/9 - 6/16. Beautiful weather. College fjiords was so clear that the captain even came on deck to view. We heard a lot of the staff say they would pick that as one of the weeks to go. Expected rain, but had very little.