I look at shafts all through the cutting process, and very early throw away the shafts I know I won't use. In this order, I look for straightness of grain, major color defects, tightness of grain. Straightness of grain is number one. Next is color defects. I don't mind sugar lines but hate mineral spots, and don't care for sap/heart variations. I let things near the joint by with no problem, but anything near the tip is bad. Next would be tightness of grain, which is a general indication of stiffness, but not a lock down sure teller. Tight grain looks nice, too.
I might add that I also pay very close attention to the way the wood cuts. Sometimes the grain will fray & fuzz up, generally indicating crappy wood. Sometimes it cuts like wax, indicating great wood. This has nothing to do with color, grain straightness or grain count. It's the quality of the wood on a molecular level, and in my opinion is the most important grading aspect of all.