Is there an appreciable difference in quality/flavor between a salmon steak vs. a fillet? I always buy fillets, but those steaks look awfully tempting, if only because they're all the same thickness!
Salmon steaks tend to have many more bones than fillets. A fillet may have some tiny pin bones left in to remove (tweezers!) but not nearly as much as steaks, with the central bone left intact. Makes sense if you think how they're cut - the fillet allows removing bone more easily. May or may not be an issue for you or your guests. (Though feeding young children, I think fillet makes more sense.)
Generally speaking, fish cooked on the bone is tastier than boneless filets, just like bone-in steaks/chops, chicken, pork, etc. Remember, stock is made from bones.
As for overall taste/quality, the most important factors are freshness and the species/variety of the salmon (chinook, coho, etc.). For wild salmon, the location is important as is the time of the year (the meat is fattier and tastier during the salmon runs). Fish use that fat as an energy source during the tough migration to their freshwater spawning grounds.
Today, the first king salmon from this year's Copper River (Alaska) salmon run arrived by air in Seattle.
amysarah brings up a good point about the convenience factor. If your dinner guests are fussy or inexperienced fish eaters, the fillets would be enjoyed more. For sure, there are expert fish eaters who have no problems dealing with bones.
The Japanese are one society that can handle this and their kids are taught at a very early age how to deal with bone-in fish. Many Americans cannot deal with any bone-in fish so this is a really your judgment call based on the people who will be sitting at *your* dinner table.
Add to that the versatility of filets. For example you might want to make your own gravalaks.