I'm sure this will start some sort of battle, but here goes...
I've looked at Coker and Diamond Back. Read specs, seeing them in person, talking to owners, etc.
Diamond Back seem to stay "whiter" longer. This is probably because of the liner they put between the white rubber and the black rubber, but I've seen it myself.
When I bought the manual to my '53 Caddie off a guy, he had Cokers on one car, Diamond Back on another. Almost the same age tires, but the Diamond Back looked brand new. He stated that was why all his tires were going to be DBs from then on. I've also noticed this on other cars at shows/get together's too. Cokers looking a little more yellow, DB's looking sparkling white. Of course, there's maintenance issues to consider, but these were cars that were otherwise immaculate, so I would assume that the tires were also getting such care. I've also heard nothing but good from the DB owners I've talked to.
Could be something to consider, might not. I only mention it in that light. Both seem to be durable enough. There was a period (about a year and a half back) where I heard a lot of bad talk regarding Cokers blowing out, but I'm assuming that was a production issue, as I haven't heard much talk like that lately.
I'm about to buy new WWW's for my 58 Edsel, and unless I can find some Firestone Silvertown's for it, they'll most likely be Diamond Backs. DB was also quite friendly and helpful when I called them for some Q&A. I haven't talked to Coker, so I can't say anything about them on that regard.
~~R.Banks