I was talking challenging content, otherwise I think talent choices don't really matter, but I don't necessarily mean cutting edge mythic. For example for a resto shaman in a 6/7hc guild, heroic imperator is challenging content. And if the guild is small, say 13 players running with a 2/3/8 setup or 15 with a 2/4/9 setup, would I advise glyphing riptide, taking high tide, and using chain heals?
No, I think using cloudburst and healing waves as Puupi suggested is the safer build, *for that shaman*, since he'll likely perform better with it.
Imperator is a long fight, and while a mythic guild which has it on farm clears it in 9 minutes, that heroic guild probably has 13 minutes attempts, so it is objectively harder to sustain mana for that long. The raid might also step on some mines which makes it even harder to sustain mana. While in ideal conditions, with extra two high tide jumps and no overheal, chain heal wins on both HPS and HPM, it requires a high skill cap to ensure this really happens, and in practice when the shaman has lower skill, using chain heals would likely make him run out of mana, and glyphing riptide won't recover the loss of the 75% initial heal.
On the other hand, with such a small group, each healer only needs to take care of about 4 players in average. Selecting the lowest HP player out of four to cast healing wave on has a lower skill cap than ensuring optimal high tide usage, and is likely to win on HPM in practice, while the extra healing from cloudburst is a nice bonus which doesn't require much thought other than using it on cooldown (though it can be optimized further of course).