Speaking from a breeders point of view here.
There are MANY brands of dog feed out there, so good, some mediocre and some that just are not worth bothering with. All of the major brands of dog feed offer a "Breeder Club" service to breeders whereby you earn points for registering the birth of your pups with the feed company and they will issue you with puppypacks for free to give to your new puppy owners when your babies leave for their (hopefully) forever homes. In return for this you provide the feed company with the new owners name and address, most give you points that you can redeem for goodies at a later date, some will send a bag of feed for free, but they are all after one thing, NEW BUSINESS!!
Now come on be honest, who can resist getting something for free? A lot of breeders are members of several such schemes, they work out who gives the best puppy packs and will happily send their pups off with these packs and they have earnt points/free product for doing so!
Personnally I ONLY feed Royal Canin, YES I am signed up to several breeder programmes with different feed companies, but I ONLY ever use the RC puppy packs, this is two fold for me. MOST IMPORTANTLY is the fact that moving home is a MAJOR upheaval for a puppy, a change in diet at the same time is even more stress on an already delicate digestive system so I prefer to send my babies to their forever home with a supply of the feed they are most used to, NOT a 500 gram packet either, you get a 2KG bag from me!!
Secondly, the RC pack is actually a very good one, a storage bucket, a lovely brush and comb for baby, and a very helpful booklet packed full of useful hints and tips for raising a well rounded, well behaved puppy, along with my own booklet as well as many more gifts.
At the end of the day, what we feed our dogs is our own decison, some are better educated as to what they are actually feeding than others, many breeders use and recommend Eukanuba, that is their personnal choice and so be it.
I guess the old saying "If it ain't broke don't fix it" springs to mind here, along with "Speak as you find", each to their own at the end of the day, but an attractive puppy pack provided free of charge by a big name company certainly looks good!!
Just this person's (very) humble opinion is all!!