Feeding your dog decent food

We got a 5-yrs old Shih Tzu a couple months ago. Are we feeding her the right food? According to http://www.buzzle.com/articles/healthy-dog-food-ratings.html, the following foods are available at Pet Smart (how the star ranking was established is not explained on that page, but based on other reviews on the web, seems reasonable):

Best:

• Blue Buffalo Wilderness ($2.08/lb)
• Castor and Pollux Organix ($2.07/lb)
• By Nature Organics (about $1.63/lb)

Very good:

• Blue Buffalo Life Protection ($2.01/lb)
• Castor and Pollux Natural Ultramix ($1.67/lb)
• By Nature (regular) ($1.45/lb)
• Wellness Super 5 ($1.73/lb)
• Nutro Ultra ($1.72/lb)

Good:

• Royal Canin ($3/lb)
• Eukanuba
• Authority

Anything else: AVOID

Ironically, the Best is not much more expensive than the Good (on average about 20% more only).