Heartsong

From a healer perspective:
I'm assuming an average cast of 2 sec, as most heals seem to be 1.5 sec or 2.5 sec. Simple math puts 1/proc chance * 2 + ICD as time-to-proc.

Power Torrent:
45 sec ICD, 33% proc chance. Roughly 51 seconds between procs, lasts 12 seconds, means ~24% uptime, or 120 intellect. Factor in that you do not get the benefit of using 7500 extra mana during the procs, and this is weaker than that.

Heartsong:
20 sec ICD, 25% proc chance. Roughly 28 sec between procs, lasts 15 seconds, means ~54% uptime, or 108 spirit. Unlike Power Torrent, you get the full benefit of the spirit gained during combat.

Hurricane:
45 sec ICD, ~12.5% proc chance. Roughly 61 sec between procs, lasts 12 seconds, means ~20% uptime, or 90 haste.

Personally, I'd recommend Heartsong for healers. I'd prefer to have spikey regen than spikey healing (since regen is going to even out over a period of time, while your healing is going to only matter until the target is at full health). Haste procs also tend to screw with my precasting, and Power Torrent just doesn't appeal to me as Int on gear provides benefits that int bonuses mid-combat do not.

While some people might not care, I think it's a shame this doesn't have a really fancy graphic like all the other new Cataclysm enchants...

Apparently, Heartsong proc IS calculated for Mana Tide :)
Source:
http://www.plusheal.com/viewtopic.php?style=6&p=85525#p85525