I believe that 1d 2d and 3d are short for First Division, Second Division, and Third Division.
I believe these are different leveled shows (just like A circuit shows for Jumpers and whatnot... and 1st, 2nd, and 3rd level Dressage shows) Though I am unsure which Division is the best.. i'd hazzard to guess First Division is the best. Its all about time qualifications and stuff.
I hope that helps (or that I am on the right track)
Yes Skippy 1D, 2D and 3D are all different divisions of barrel racing. 1D is the best division you can get into. The IBRA States that, "1-D: Fastest time in the class and those who qualify for this division.
2-D: Fastest time in the class plus ½ second and only those that qualify for this division.
3-D: Fastest time in the class plus 1 second and only those that qualify for this division.
4-D: Fastest time in the class plus 2 seconds and only those that place in this division. Rider must make a good faith effort to run the pattern as fast as their ability will allow. "
Its hard ot get a 1D horse for anything less then $15,000, they're high money earners and hard to find for sale. I hope that helped some