223- Benchmark not only has it shown superb accuracy for me it meters as well as a ball powder.
22-250- H4895, meters fair and has shown the best accuracy.
243- Varget, for lighter bullets and H4831SC for 87 gr and above. In general people do not consider 4831 a 243 powder but accuracy with 87, 95, and 100 grainers has been phenomenal.
I have no experience with the 6.8. Many other powders will give superb results, these are just the ones that work best for me.