Good morning and welcome!
I am a breeder and in my studies of the breed, the original standards for Labradoodles include a boxy head (really...!) and a more broad chest, much like that of the English Labrador.
I don't know that anyone has come right out and said that English is preferred over American, but in my opinion, if you are striving for the "recommended standard" of the Labradoodle, you would consider this as an important factor.
I have two F1 Labradoodles, and they are siblings...however one takes after the Poodle side and she is lean and narrow in the face and shoulder area, the other takes after the Lab and I believe that her pedigree has English Labrador in it because she has a very nice head and chest for the Labradoodle standard.
I got most of my "standard" information from ILA (
www.ilainc.com) and from the Rutland Manor site.
Hope this helps...still, much of the "preferred" look is a matter of personal taste and since these dogs are still evolving, you can find just about anything to suit your taste.