As shadow priest what's the most suitable stat between haste and crit?
Short answer: Haste
Longer answer: Haste is roughly a 20% larger dps gain per point than crit:
2.92 dps = 1 int. Hit/spi = 0.37 int. Crit = 0.4 int. Haste = 0.5 int. Mastery = 0.39 int. Spellpower = 0.79 int.
(those also show why you shouldnt gem for hitcap)
Haste is far better.