That's a tough call. I've seen many cows from the lines more known for milking that are not good producers and have seen outstanding cows from lines that aren't known for milking. The more female relatives (or pics) of the bulls you can see, the better. A heifer's udder generally (but not always) resembles her paternal granddam's udder.
Also, the first bull you mentioned is horned while the other two are polled. So, you will have to decide if you want horned or polled calves. If it were my choice, going by the pedigrees only, I would most likey choose 15954, as he has quite a bit of Woodmagic in his line.
These bulls could carry dun, do you know if they have been tested?
Probably the most well known milking lines are Cornahir Outlaw:
http://www.dextercattle.org/pedigree...&Page=1&Sort=0
And Lucifer of Knotting:
http://www.dextercattle.org/pedigree...&Page=1&Sort=0
If you look at this page of my website
http://www.lazyj5dexters.com/Milk.html
you will see 3 of the Dexters I've milked over the years. The first one is Crystal Star's Eileen.
http://www.dextercattle.org/pedigree...&Page=1&Sort=0
I called her my little black Jersey and that was just how she looked. She had a beautiful udder and teats and was easy to milk.
Second is Elkhorn Sweetie.
http://www.dextercattle.org/pedigree...&Page=1&Sort=0
Sweetie is now owned by my friend who has been milking her for a few years now.
Third is Shome Shena.
http://www.dextercattle.org/pedigree...&Page=1&Sort=0
Not the largest udder, but very well balanced and nice teat placement, and good suspension.
Hopefully, this will give you some idea of the different lines. But, as I have found over the years, it's kind of a crap shoot, and you never know just what you'll get.