Long term, it is probably best to stick to Spiritshift forms that have some utility beyond auto-attack. Of those, I would think Wolf is the best (speed/knockdown), or possibly Boar for the regen.
Thinking about it, I wonder if the Wildstrike talents apply to any spell damage if cast while Spiritshifted? I probably won't get to check til this weekend though. If there are any spells it does apply to, that might keep Spiritshifting at least slightly relevent in the late game.
Might also be interesting to build a melee Druid as a two-handed weapon user, looking to lean on Firebrand which has some interesting properties (primarily of which is that it apparently targets Reflex instead of Deflection, and Druids have several convenient ways to debuff Reflex). For talents: Soldier weapon group, Two-handed style, bonus to Fire damage, bonus level 2 spell... am I missing any others?