With a 5x shaman group, the heroics I've done so far easiest to hardest:
Grounding totem is the most important totem next to stoneclaw in all of these.

Mana-tombs: First boss is a DPS race and second boss is an endurance fight, spread out for second boss because he does a 1shot cleave, 3rd boss is a joke, 4th boss(Yor) hits extremely hard and reminds me of the last boss to Slave Pens (use potions)
Rating: 2 (really need ALL earth elementals for the second boss which can cause you to wait around for 10 minutes)

Botanica: Use all earth elementals on the first boss, only the last boss needs them all again, and it will be up by then, rest of bosses are a joke, trash hits hard before first boss, use chain heal when they shield.
Rating: 3 (first boss and trash before first boss can be a pain)

Underbog: Pretty easy, I was expecting something more difficult, I still dislike the dungeon because it is so long, second boss hits moderately hard
Rating: 5 (last boss can be a bitch if he levitates at the wrong times or spawns too many adds)

Slave Pens: Last boss is really really tough, he hits extremely hard and will oneshot earth elementals, try the best you can, endurance fight, use mana potions
Rating: 7

Mechanaar: First boss is easy and so are the minibosses... 2nd floor trash hits too hard and is likely to wipe you, the gauntlet event is extremely difficult, expect many wipes after the first boss.
Rating: 9

Sethek Halls: Alot of trash not worth doing, 6 pulls of ravenguards before the last boss is a nightmare, they oneshot shaman. First boss is easily doable if you need a drop.
Rating: 9

As far as gear level, my shaman have 850 spell damage, 8700 hp, 8200 mana, and 15% crit unbuffed