What to feed a dog can seem to create stronger and more vociferous opinions than global political issues! Opinions vary widely and the base line as that almost any food in a shop has been approved as providing adequate nutrition -- but from there, you can go from mediocre to ultra-yuppyish, costly foods with exotic ingredients, not to mention the wars between raw feeders vs. everyone else, anti-grain people, pro-holistic foods people... dog food advocates can be like noisy religious advocates, each trying to win converts to their faith.
This is a useful link that explains one opinion on how to choose a food, how to interpret dog food labels, etc:
Another detailed site:
This is a useful tool: a dog food ingredient comparison chart. You can compare four foods or treats at once, and click into details on each ingredient.
What makes a good treat? Here's some do's and dont's for chewers: