If you are willing to spend between $10k and $30k (depending on the route) and wait ~2 years the AK workshops by Marc Adamus are hard to beat. Whatever you may think of his processing style, the places he takes you are difficult to get to on your own without substantial expense and logistics hurdles. And even if you have the money to pay for helis, raft boats, and/or snowmobiles, you still need to know where to go, and won't learn half as much as you would on his trip.
I have been on his winter and summer trips. Of these, IMO the summer is a far more breathtaking experience, but also considerably more costly. You spend time camping on small pads in the Juneau Icefields, barely large enough to land a heli, with breathtaking scenery and multiple flights over the icefield itself. And if you have serious money to spend, he does have expeditions with float rafts up the rivers, meeting up with helis that fly in from BC that sound amazing... but too expensive for me.
I am not a great fan of his winter AK trips. Compared to what he does in BC the scenery and terrain is not nearly as diverse, though it is far more remote, with A LOT of driving all the way up to the Attigun Pass
Never been a fan of fall color photography so I can't speak to those. From what I have heard they are similar to the winter ones - mostly car based supplemented by helis.
Disclosure - I have no financial interest in his outfit, other than to give him more money than I should about once a year. Here is a view from one of the camps on his summer trip. Homework assignment - find the figure to get a sense of scale.
