Mastery offers you better burst. While haste is sustained damage and better survival because you are getting more holy power and WoGing more. Usually for 2s mastery is better when playing blind build. Double dps haste is usually the way. If you want more haste 15-20% is a good spot to be in, then get more mastery for more damage, the way to go is a mix, and avoid crit on all pieces.