The 3 things you'll want from a trinket are haste, mp5 and spell power. Starting out new, I found that I would run dry on mana quite quickly. Now that I'm geared I don't have the problem, so I'm trying to get as much haste/sp as I can. Haste cap for Shamans is just over 1200, so feel free to stack haste through the roof without worrying about hitting a cap. SP is a good stat, but personally I find that many of my heals were overheals anyway, so I concentrated on more haste for some quick heals in a crunch.
One quick note: I should broaden my mp5 term to say anything with mana return or that saves mana. For example, the trinket you have has SP and a proc to reduce mana usage on next spell. That's exactly the type of thing you'll want to go for as a resto shaman.
Generally speaking,
Undergeared: Haste>Mp5>SP
Geared: Haste>SP>Mp5
Just remember, haste is king.