I usually do damage, end, accuracy in order of most to least emphasis. The reason I emphasize damage is because Mud Pots attack pulse is about the only damage you have that's not slowed by Granite (because it's a toggle). Yes, it doesn't do tons but it's steady while you do other things.
Then end because endurance is a problem when you're running a bunch of the pre-Granite toggle armors, and MP costs a lot.
Then enough acc to be relevant.
I don't worry too much about its taunt value. Gauntlet from my other attacks will assist, MP's own slowing tends to keep foes in the area of effect (if I do somehow lose aggro from them, they'll stay close anyway and get re-aggroed soon) and I usually take Taunt on my Stone tankers anyway (helping to offset their poor mobility).
Also, nitpick: Endurance Modification enhancements are for powers that increase your end recharge or drain enemy endurance. Mud Pots takes Endurance Reduction enhancement.
Edit: once I looked to IOs, I'd start thinking about slipping a proc or two into Mud Pots for Even More Damage. Procs in toggles only activate once every 10 seconds, but Granite Tankers kill slowly enough without assistance that that isn't so much of a deterrent (and Granite Tankers *with* assistance don't usually need to worry about killing speed).
If we are to die, let us die like men. -- Patrick Cleburne
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The rule is that they must be loved. --Jayne Fynes-Clinton, Death of an Abandoned Dog
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I usually do damage, end, accuracy in order of most to least emphasis. The reason I emphasize damage is because Mud Pots attack pulse is about the only damage you have that's not slowed by Granite (because it's a toggle). Yes, it doesn't do tons but it's steady while you do other things.
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Agreed, but I'd cap dam & end redux, both at the same order of priority. Oh and run Herostats and tell me Pots doesn't do a "ton" of damage compared to your other powers, in or out of Granite. 
Damage auras are always overlooked by ppl who only look for the big orange numbers, but they're almost always among your best attacks for overall numbers and even end efficiency, as long as you're playing correctly (i.e. not concentrating on 1 mob at a time--gather them around you!).
Oh, and single proc comes out to about 16.6% of the total damage an ED capped (for damage) Pots does, which comes out to the same as a single SO, so it's a tradeoff bet. slotting for damage or a proc. Of course, the correct answer is max out damage & end redux, and then proc away.
My slotting at 50:
Multi Strike D/E
Cleaving Blow D/E
Scirocco's D/E, A/D/E, Proc
Eradication Proc
You can also fit in an Impeding Swiftness proc, but it's smashing (as is Obliteration) and I wanted Eradication's energy damage. Scirocco's is lethal, but get's me a bit more neg resistance. Obviously, if you can afford it, stick in the Armageddon proc for a higher chance to hit.
An Offensive Guide to Ice Melee
3 EndRed and 1 Taunt. It requires nothing else to fulfill its role.
There are no hard iTrials, only hard peo-... er... wait.
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3 EndRed and 1 Taunt. It requires nothing else to fulfill its role.
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Disagree strongly. Adding Acc and Damage to it can be a big help. The Debuff and base Taunt duration should keep anything but another Tanker from stealing aggro from you.
Let me never fall into the vulgar mistake of dreaming that I am persecuted whenever I am contradicted.
~Ralph Waldo Emerson
"I was just the one with the most unsolicited sombrero." - Traegus
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3 EndRed and 1 Taunt. It requires nothing else to fulfill its role.
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Again, you should play with Herostats running just once to see how much total damage Pots does. Even unslotted for damage, as you undoubtedly have it, it'll likely surprise you. And considering for 4 slots (the same as your suggestion) you can fully ED cap end redux *and* damage, I see no possible reason why you wouldn't want to maximize its significant damage.
An Offensive Guide to Ice Melee
I'm new to Stoney tanking, what the best way to slot Muddy Pots while leveling to 50 and what is best once you hit 50? There are so many choices:
Enhance Slow
Enhance Damage
Enhance Accuracy
Enhance Taunt
Enhance Endurance Modification
at 50:
Enhance Slow
Enhance PBAOE damage
Thanks!!!