Interesting question regarding availability. For average number of manufacturers, I would say it would be a wash between the 260 and the 6.5 creedmoor. For the 260, Remington, Lapua, Nosler and Norma make brass. For the 6.5 creedmoor, Norma, Nosler, and Hornady all make brass. For the 6.5x47, Lapua, to my knowledge, is the only manufacturer that makes that caliber.

However, the 260 has an edge over the 6.5creed and the 6.5x47: one can easily neck up or neck down any 308 based cartridge to make 260.

As far as which one is more inherently accurate: I don't have enough data between those three to say. I do own a 260, and it is boringly accurate. It doesn't care about the seating depth, velocity, or powder that I've tried. The 2 bullets I've tried are the 140gr berger hybrid and the 140gr Hornday soft nosed bullet. The difference in group size at 100 yards is hard for me to distinguish.

If you want a DBM system and be able to seat the bullets out as far as possible, get the 6.5x47. The 6.5creed will be about in the middle with overall length, with 260 being the longest of the three, all things being equal.