Imo always go for advanced refinement runes because you need more of them than medium and they are harder to get, whereas medium is more common. Save up another 600 adv refinement runes and use them during the next rebate should get one of your gear to lv 10.

He wants his first position to be fastest, all his equipment for 1 character is already lv 6. 144 is already enough to get 2 equipments to level 7. 3 remaining equipment will only require another 240-300 max medium refinemnet. After that he will need 1700 adv for 1 equipment to max. Always get adv whenever possible. If possible Save up another 600 to get 1200 adv and use it all on the helmet to max that out (all at once during refinement rebate) because it gives % of initiative.

He will only need another 350 medium at most for his 1st position, while he will need around 1200 adv refine/ equipment to max one, which is 6000 for 1st position. In addition medium are so much easier to come by than adv. Also it is much better to max 1 item rather than level them equally.