Confused on what food to switch too

[Saber]

Hi, I'm new here and have been reading all about dogs foods but am still confused about whats the best food for my pup.

I have a 6 month old puppy that my parents adopted on Nov 29 for me as a christmas present. They wanted me to have a "small" dog but we walked out of the pound with a pit/shep or lab mix.

He is on the Science Diet large breed food right now.
and I am confused about this food. I have my vet and a few other people tellin' me its very good and then I have others saying it's just a high priced low quality food.

I've been wanting to change his food for a few weeks now because Science Diet is pricey but I do want him to have a good/high quality food.

I've read Innova, Solid Gold, Chicken Soup for the Dog Lover's Soul, Canidae, Blue Buffalo, California Natural, Natural Balance, Nutro Natural Choice.

All are good ones? plus Blue Buffalo, Nutro and Natural Choice, are sold at petsmart.. Which I like since I don't live too far from it.

But what food should I swhitch him to?
which one would be best and not so expensive.