There are several options depending on which salmon species you're targeting and where (that is the conditions) you are targeting them.
Reds (sockeye) runs are probably the most prolific and longest lasting runs of the salmons. A good 7wt set up works great on them. Just about every stream, creek, river, etc. holds reds. Now, they normally don't actually eat during their runs, rather they are most often caught by dragging your fly across the bottom and hooking one. Snagging is of course illegal, but the reds are often so thick in numbers in areas that you simply can not avoid hooking them. Fresh caught red salmon on the grill on an Alaskan streamside is one of the greatest experiences any angler can experience. Highly recommended.
Silvers run a little later than Reds and generally are larger in the 13 to 16 pound range. In many areas of Alaska, the really big numbers of silvers are just now showing themselves. I have used 10 wts, 9 wts, 8 wts, and 7wts on the silvers and my preference for all around would be a good 9 wt. Silvers readily take flies and one of the most exciting ways to get them is on top water poppers. Its hard to describe the excitement of 15 pound silvers crashing those top water flies. One of the truly most amazing experiences of any fly angler.
Kings run early compared to the others and best runs are generally over by early July. They aren't called kings for no reason with size ranging from the "small" jacks at about 15 pounds up to the mature fish that can easily exceed 50 pounds. The kings will take flies...but in my experience you have to work at it. Big flies, articulated and with lots of color, work best for me. To throw the big flies required you really need a 10 wt...and honestly no fly rod, even a 12 wt is going to turn a big king salmon(50 pound class) in a small stream. I have successfully chased big kings for several miles in a river boat after hooking them and watching them run. They are one of the most powerful fish that you will ever encounter in fresh water. Even the small jack kings are terrific fighters. I suppose a single handed 9 ft 10wt is probably the best all around choice for kings, however in some situations the spey rods up to 12 and 13 ft can really be effective...and save wear and tear on your body. 8wt and 9wt spey rods are ideal for this application. This is a somewhat specialized technique...but it is very popular in certain locals in Alaska where you can't get in a backcast because of vegetation or whatever and/or the water to be covered is larger than what you can cover than by the traditional single handed rods. IMO, king salmon is pretty much the top freshwater fish in the World for the fly angler...but may not be ideal for the beginner.
Pink salmon have shown up in my experience on small streams relatively early in the year and run 5 to 10 pounds with 5 pounds being much more common than 10 pounds. They are fun to catch on flies and 7wts are more than adequate for handling the flies and fish.
Chum salmon aren't in my experience base...that is, never targeted them and never caught them even accidentally. They are not a preferred eating fish and are largely used by the locals as dog food.
So, what's your target pleasure?
Summary: As for a general purpose set up...it would probably be a 9wt with floating line and various sinking tips to match the stream conditions. The Rio versa tip is absolutely outstanding and indispensable for covering multiple type stream conditions. The larger the fish, the better the reel you will need. However, I have had reds in strong current completely strip an excellent reel and , of course, with kings in relatively small streams you better be prepared to chase them....or loose everything.
Definitely go to the Great Land! There is nothing like it.