I've cruised on both lines extensively, to Japan on Celebrity.
The quality of the cruises is very close and I don't think you can go wrong with either one.
You may have to compare the ships to make a decision.
As MrCruiser stated, the theatre production shows on Celebrity are much better.
The crew on both ships come from Indonesia and Philippines but beyond that, Celebrity has many eastern Europeans mixed in.
Celebrity has many Greek Officers whereas HAL has many from the Netherlands.
We liked the food better on HAL than on Celebrity and the service is exceptional on both lines.
We have cruised on HAL 10x since September of last year and loved the HAL entertainment other than the shows.
Compare the ship layout, the ports to be visited and the roll calls of the ships that you are comparing.
Japan is an amazing experience.