If you could smoke any kind of Alaskan salmon what would you choose for best flavor that would retain some moisture and not to dry?

King, then sockeye.

King, for second I would choose fall steelhead over sockeye.

Yukon River Chum salmon have a higher oil content than reds and even higher than Kings in some places. Reds are very dry compared to Yukon chums IMO.
Our Kings are too fat to just smoke they just drip Forever, and turn into a puddle of oil, so strips are better.

Some cold smoke dry King slabs sliced very thin that are good too.

I have always found that interesting, Jeff. The rivers here are relatively short compared to the Yukon, with the exception of the Stikine and Taku systems.
Our chums are pretty nice when they first come in from the gulf. They stripe up and deteriorate fairly rapidly from there out. Our kings and reds are the superior salmon, fat content wise. The fall steelhead are pretty amazing, IMO.
Again, kind of interesting the difference, regionally.

I've had great smoked king silver and red. The best smoked salmon I ever had was red strips, used to be called squaw candy. Somebody in Perryville made it it was amazing. Around here reds (sockeye) are the most abundant so the most smoked but I hear a lot of people mention smoked coho and smoked king is always good. Hard to go wrong with any of it really but if you're talking moist I would say king or silver. If you just smoke the ribs and belly it will be more moist than the tail or back sections. Lots of fat in the belly.

Regionally AND personal taste preference

The Nuahagak kings had a inch of belly fat this year.
The reds were so plentiful and also considered the best smoked because it is or is the premium salmon I most mind.

On my river, the Nooksack it is the chum for most people, because they would not eat it fresh.

The little chicken coho that make it though the Indians nets are good. Leaner, less oily like some want and lots of them

Non salmon
My fish would be our winter run, wild steelhead. Firm with just enough fat.
That fishery has been closed for years.
Or Columbia river white sturgeon from the Boardman pool

So personal preference and location

Thanks for the interesting reply's. For me in Montana I have limited access to Salmon depending on the market availability. Right now sockeye is the most common. King which I prefer over the two is more costly and not as available. Sometimes we can find silvers but none this year. I have been holding out on smoking sockeye hoping to find something else. We have mountain whitefish which is good smoked.

Was able to find a small amount of king filets today. The store did not get much in but they had it in their weekly special flyer which sale started this morning. I was there first thing. Not sure they really wanted to even sell it as they kind of had it hidden like gold. $8.98lb for fresh filets.

It is interesting. The Yukon River Chums travel as far as 2,300 miles upstream to spawn. They go up smaller clear water rivers draining into the Yukon. I am 70 miles upstream from the mouth of the Bering Sea and the fish going past are dime bright, no bars and sea lice on the early ones.

They have 3-4 times the oil content of any other Chum salmon. They also have the most omega 3 fatty acid of any other salmon species.

The Yukon Kings are 30 % oil. average King in other places is like 10% or less.

I caught Chums in Homer in salt water once. Not the same fish, the meat was pale and mushy.