It depends on what you like and who you'll be with.
If you have kids, are on a budget, or only want to use 1 TS credit on the dining plan, go to Whispering Canyon. Pretty good menu selection including an "all you care to enjoy" skillet. I've been there for both breakfast and dinner and both were very good. It's one of the more entertaining places for children to go, there's wooden horse races, and different "cues" the servers will play off of like asking for ketchup.
If you're going in an all adult party, don't have a strict budget or don't mind splurging, or have an extra TS credit, go to Artist's Point. This is personally my favorite restaurant on property. The menu is what I've been calling American exotic. There's venison potstickers and buffalo steaks on the menu, as well as tamer things for the less adventurous. The menu changes based on what's in season.
This all isn't to say you couldn't go to Whispering Canyon with all adults or to Artist's Point with little kids, just that they may not be as appealing. Whispering Canyon can be loud and have lots of kids running around, so if you're looking for a quiet place, this is probably not for you. If you think you're kids wouldn't be able to handle a more "upscale" place or would be bored with it, I'd say steer clear of Artist's Point, but children are welcome and they do offer a kids menu although my understanding is it's not very extensive. Allears.net has menus for both places so they might help you're decision.