I do mixed cores, aboo on the back, maple on the belly. I do it because aboo is stronger in tension and maple is stronger in compression. To each their own, they all work and most would be hard pressed to tell the difference in otherwise identical bows. Fond of walnut too, for the look, but it seems to have a higher failure rate than the others, seemingly because it drinks glue. Haven't had one fail on me yet, but have seen issues with other folks.