Blackberry Plants - No Fruit on Some

[BOB6831]

I have noticed for a few years now, in an area where I have maybe a total of 30 blackberry plants (have transplanted from several different places I have visited over the years (mostly golf courses), that maybe only 1/3 to 1/2 of the plants produce fruit. ........... Note that I follow the same procedure on all the plants. I cut down the 2 year old canes (brownish-dead canes) in the fall (or in early spring), so the new canes are only ones left.  I live in upstate NY. Any opinions on the sweetest blackberry that will grow well in this area would also be welcome. I am considering Triple Crown, Ebony King, Kotatas, Marion, Chickasaw, or Chester.  I planted some thornless blackberrys (from mail-order catalog) a few years back, and they are big and produce a lot of berries.......... BUT are sour!!!!  I have a dilemma with those plants..... I hate to pull up-kill something that is producing so well!!  So, I really want a good, sweet blackberry that can eat right off the vine, thorns or not. Thx.

Bob