It doesn't matter what type of equipment you refine, they all will give exactly the same bonuses - secondary stats, only affected by purification % and refinement lvl.

The most efficient way of leveling up your refines is doing 6->10 in one go, but to be safe you need to have saved 1350 adv. refines. It's 1400 for 7->10 and 1300 for 8->10. I know saving resources isn't really liked by some of the players, but it can be really worth it in the long run.

I counted them. Without counting it's 1700 for 6->10 or 7->10...