I happened to come across this thread while searching for something else and thought that I would bump it up for further discussion. I have heard this statement "buy the koi not the breeder" a lot and I agree with it to a certain extent. However, I feel that it would be a big mistake to depend on this statement alone when purchasing potential tateshita or tategoi. My experience, albeit very little, has been that when I buy koi from less well known breeders with very little history on the bloodlines that they use, the koi usually don't pan out as I had hoped. As a result, now I usually start with the breeders before I look at the koi.
Not to deviate from the topic of this thread, but I think that the top 4 kohaku breeders are (in no particular order): Sakai Fish Farm, Hoshikin, Toshio Sakai's Matsunosuke, & Dainichi. When it comes to kohaku size, the first breeder that comes to mind is SFF. I don't know how they do it but when you can get a nisai to be 22-24" then you have gotta be doing something right! When it comes to skin quality and pattern, Hoshikin's gotta top this list (Tomoin bloodline influence?). When I hear Toshio Sakai's kohaku, the two things that come to mind are beni quality and scalloped kiwa. Dainichi, well, anybody's gotta love Dainichi's koi. Anyways, these are just my opinion and I hope that others will shed more light on this topic so that we can all continue to learn.