Why not do both? Sub as the first order and dilution as the backup in the event the sub does go wrong.

But as long as you practice, subbing can be as easy as a walk in the park.

When doing Dilution techniques, dont forget the important step of creatine-loading at least 3 days prior to the U/A. Read up on the Dilution "sticky" thread (disregard the aspirin step though).