One of the smartest members of the priesthood has done an excellent write-up of how crit and haste play out in practice. Well, in theory. In theoretical practice. Go check it out—Zusterke has done a splendid job of exposing the interlocking mechanics of these two stats.
He's concerned primarily with tank-healing throughput, which is of course what these two stats are all about.
TL;DR? Not sure I want to do this at all, because the article is not that long, and it's very well written. He quickly shows how a balanced profile gives the biggest boost to HPS, but that crit is slightly superior overall. Don't just take this over-simplified conclusion for granted though; his article is very nicely done and a fascinating read. I love good thinking!!
Enjoy, and have a safe & happy new year!