First off let me start by saying I am a shaman healer and have been healing almost exclusively heroic PuGs. I have only grouped with my guildies 3 times so my experience and preference of H instances is from grouping with PuGs via LFD.

I voted for H Stonecore. Reason is because there are so many ways to wipe the group on the first boss. Here are the ways:
1) DPS doesn't know or have insufficient aoe dps/mana to kill the crystals.
2) somebody fails at running from dust (sometimes its me due to lag or adds whacking away at me cos tank is unable to pick them up)
3) insufficient dps on boss extending the fight way longer which causes me to run out of mana.

Usually its no 2 that wipes the group. I usually wait and see if the group wipes on the first pack of mobs (which in H Stonecore's case is quite hard) but nowadays I don't even bother to try, when i get H stonecore as my random H I leave immediately saying "sorry guys this instance is hard with a PuG".

Below is a healer's perspective and rating (1-5 with 5 being hardest) on the difficulty of H instances with a PuG.

1) H ToT - First boss is very hard to heal if the group doesn't bother to avoid tornadoes. Tornadoes takee almost 70% of the person's health. Second boss is easy as i can hero which helps a lot. Third boss is a b**** to heal as dps is damn poor in PuGs which means adds are taken down much slower. I'd rate this a 4.

2) H Grim Batol - First boss is not too bad. I usually help CC the purple add and because hex allows for a certain amount of dmg before it breaks the add is usually at 50% when it breaks. The second boss is also not too bad. Usually it takes a wipe for caster dps to realise that I really mean it when I tell them before the pull that when he puts on his shield they have to get within melee range to avoid fire. Third boss is the killer in this instance. All dps having to switch to elemental because their dps is poor causes the fight to be extended. The breath is so wide that usually all range will get hit even though i tell them to take all the corners but they move to the middle to get in range of the fire elemental but forget to run back to their corner. Usually the breath is hard to heal cos the tank will take lots of dmg after the breath and its a decision of healing the tank or healing the casters. Last boss is easy if ppl just STAND IN the eye of the tornado and if u're in there but taking dmg you're not doing it right! I give this instance a 4.

3) H Lost City of Tol'vir - You missed this one in your poll btw. First boss easy but tanks always LoS me... Second boss is freaking mana intensive as baby crocs go down so slow due to poor PuG dps. Third boss is ok if ppl get out of the WHITE CIRCLE! Last boss is quite hard as well especially if the group is melee heavy. I give this a 3.5

4) H Blackrock Caverns - very easy to heal if group is competent. I've been quite lucky with this instance as 2 out 3 times i got it as my random i've gotten competent PuGs. First boss is easy. Second boss i barely have to heal. If ppl screw up then its usually a wipe. Third boss is the killer if your tank sucks. I've had a tank which knew this fight and did so well that I needed to put down just 2 healing rain and a few healing waves on the tank. I've had a tank who was geared but didn't tank as well where I was oom at the end. Beauty is easy. Last boss also easy. Haven't had a problem healing kiter and tank. I give this a 3.

5) H HoO - I can heal semi competent PuGs through this instance. First boss is pretty hard if the strat is not right. I've encountered numerous strats for this boss. Whole group jumps down or tank and one dps jump down or 2 dps jumps down on either side (this one usually is a wipe). The other hard boss is the shadow boss if the tank doesn't know to kite. I give this instance a 3.

6) H Shadowfang Keep and Deadmines - easy but long instances. First boss for SFK is hard if interrupters fail. Other than that easy. i give these instances a 2.5 and 2 respectively.

7) H Vortex Pinacle - is the easiest. Certain trash in this instance are harder than the bosses. First boss easy. Second boss, if ppl don't get thrown off the platform, is easy. Third boss is easy.

This post has been edited by B@rt: Jan 12 2011, 04:32 PM