1.Would you feel that paying 4 times as much for one over the other is justified and if so which one. ?
I wouldn't buy either one, the first one has a good level of protein but the ingredients are pitiful :| why not just boil up some rice?! as for the second one, ingredients seem much better but the protein level is much higher than I would like.
2.Would you choose to try the most expensive or the cheapest first?
All depends on the ingredients and protein levels.
3. Do you choose your dog food based on something else?
I won't buy a dog food that has corn or a high amount of any other 'fillers' (just a waste of money!). Wouldn't buy anything with by-products either : and because I'm getting a giant breed (Mastiff) Protein and fat levels are really important so I'm going to stay away from anything with a protein level over 24%