nice and ionice: which one should come first?

I need to run some long and heavy commands, but at the same time, I'd like to keep my desktop system responsive. Examples: btrfs deduplication, btrfs balance, etc. I don't mind if such commands take longer to finish if I give them a lower priority, but my system should always be responsive. Using nice -n 19 and ionice -c 3 should solve my problem, but I'm not sure which command should come first for maximum benefit. * Option A:

nice -n 19 ionice -c 3 btrfs balance start --full-balance /

* Option B:

ionice -c 3 nice -n 19 btrfs balance start --full-balance /

Is there some subtle difference between options A and B? Are they equivalent perhaps?