Abec is nothing more than a tolerance rating for measurement and precision. Abec 3 to 5 is my preference. Then you have your inner and outer races and the material they made of, then how deep the groove is that the balls sit in and then finally the material the ball is made of.
Ceramic = less friction and much higher heat tolerance but also more fragile.
Steel = More friction, lower heat tolerance but much stronger
Then of course there is hybrids but the balls themselves are not Hybrid, either the balls are ceramic or steel and the race is either steel or ceramic.