Help! My cav will only eat Pedigree Dog Food!

My cavalierpuppy Tucker (7 months old) has a healthy appetite when he likes something, but is very picky about what he likes, LOL. When we got him the breeder had been feeding him Science Diet puppy kibble with a topper of Pedigree Ground Chicken dinner. Now, after researching the brands and finding that Pedigree and Science Diet are not the healthiest dog foods on the market, I've been trying to change him over slowly, in increments. That is, 1/4 "good dog food" mixed with the Pedigree. He has turned his nose up with even the slightest bit mixed in his beloved Pedigree. I'm looking for suggestions and help. I live in the US, and like to get his food at Petco, although with the Pedigree I have to go to the grocery store to get it, of course. My question is: Should I just keep him on the Pedigree since he likes it, or should I be adamant about finding another food that he will eat but is healthier? He doesn't seem to like any food that has a sweet potato or fishy taste so I know that leaves out a lot of the more wholesome dog food brands.
Here's what we've tried:
1) Whole Earth Farms: He will eat the puppy kibble, but will not eat either the puppy canned food from this line, or the Chicken and Turkey. There is a sweet potato element to both of the wet foods that he doesn't seem to like.
2)Nutro...didn't like
3)Canidae...hated.

Please help! Thanks in advance.

Try Stella and Chewy's -- that stuff smells so good I'm sometimes almost tempted to eat it myself. Skippy eats a combination of that and Merrick Grain Free kibble, but once the last bag of kibble runs out we might switch to this -- http://justfoodfordogs.com/

Don't change his food so much. If he doesn't like sweet potato or fish, thats OK, there are a lot of other good choices. Put his food down, with no fuss or begging. After 15 min pick it up, then give NOTHING ELSE INCLUDING TREATS until his next mealtime. Don't worry, he won't starve himself. However, always have water available. Continue this way and in a day or two, he will be eating every meal you put down.

I agree that Science Diet and Pedigree aren't the best foods. That being said, I give Bella and Milo Merricks grain free kibble. I mix in a teaspoon of plain Greek yogurt with some steamed chicken breast.

Joyce is perfectly right. I have had dogs for over half a century now, mostly Cavaliers. I decide what's best for them and feed that. End of. Tough love but the eat it or go without rule really works.