Continuing with the Shaman. I will compare a Wis/Con shaman with a Wis/Cha Cleric.
Basic hit points, healing surges, number of skills, are all the same.
Spirit Boon is distinctly worse than Healer’s Lore, since not only does it involve moving around the spirit companion, but it uses a secondary statistic rather than a primary statistic. Healing Spirit is a bit less convenient than Healing Word, since you have to maneuver the spirit companion around. However, the two of these combo when you can get two allies next to your spirit companion, effectively doubling the benefit of Spirit Boon. This also makes noncombat healing more efficient. I think I’d still prefer the convenience of the cleric, but it isn’t a big advantage.
The Shaman has Con rather than Cha as a secondary statistic, a nice benefit. But the Shaman has to spend a feat to get Chain Mail proficiency, which cancels this out. But also, the Shaman has to take Str 13 to qualify for this feat, which is not difficult, but still inconvenient.
Channel Divinity with Turn Undead is a very fine ability. Speak with Spirits is hard to compare because it depends on what kinds of noncombat checks the DM allows it to be used on. If the interpretation is restrictive, and it can only be used on checks that clearly take exactly one round to perform, it is mostly limited to combat checks and doesn’t seem better than Channel Divinity. If the interpretation is expansive, and the shaman gets a major bonus on almost every noncombat skill check, this power is a very potent noncombat ability worth many feats. I’ll assume a restrictive interpretation, so the cleric is a bit ahead.
The shaman has some fine at-will powers, but I think the cleric’s Sacred Flame is better than any of them, and that’s even without the fact that it does radiant damage. The shaman has some cool encounter powers, but I think the cleric’s Divine Glow puts it on top. The shaman may have a bit better utility powers (his L2 powers are better than the equivalent cleric powers).
The cleric has no melee powers, nothing to do when pinned. But the shaman can attack through the spirit companion in this situation, a big advantage that may compensate for the cleric’s better powers. However, it is a drawback that the shaman sometimes has to maneuver the spirit companion around in order to attack at range. Nevertheless, the shaman's flexibility makes up for a lot.
When it comes to daily powers, the cleric’s Consecrated Ground is broken. Assuming the DM fixes it, both the cleric and the shaman have some great daily powers. Wow, that Spirit of the Healing Flood looks mighty. But overall, I don’t know who is better.
At this point, the classes are close, perhaps the cleric is still slightly ahead.
Finally, the shaman has the spirit companion with its ability to block a space and perform the Spirit’s Shield opportunity attack. The shaman has lots of different things it needs to spirit companion to do, so placing it seems non-trivial. And Spirit’s Shield is not going to be very useful in the situation where a summoned creature would otherwise seem easiest to use (tying down a melee fighter at the beginning of the battle). But gosh, compared to the various minor advantages of the cleric, the chance of getting the equivalent of additional attacks without spending actions is pretty mighty. In particular, it a summoned creature is anywhere near worth a daily spell (as it is for other classes), it would have to be pretty mighty. I’ve never played with a summoned creature, though, so it is hard to judge the tactical consequences.
So whether the shaman or the cleric is better depends on how the DM interprets certain abilities and how the tactics of the spirit companion work out. Under the assumptions I’ve made, I’d say the shaman is better, but it looks like there is something to be said for either one.