This is an interesting question. It'd be great if there was a baseline rule of thumb to follow, but there are so many variables to consider during a fight that would effect whether hard-casting or SB:SS is better.
So lets run down the scenarios that you listed and see if we can give some general advice. I think I'm going to end up generating more questions than answers, but hopefully the theorycrafters/masters of the universe can come by and give us the low-down on the most efficient methods in terms of damage output.
Scenario 1: 3 Shards, Both trinkets proc and you react by casting DS. Fighting Patchwerk.
I definitely run in to scenarios where I have 2-3 shards banked before a DS because I try to only use Haunt when I have an intellect proc (usually at least 2 if I'm being picky). Luckily all my procs are intellect ones so this becomes pretty easy. Now for your first scenario you've got both trinkets proccing at the same time which means they've been on ICD for a while. So if you do what I do, then it's likely you haven't had 1-2 +int procs to cast a Haunt on meaning you've been banking shards.
This would be an absolute dream scenario to come across since you are almost getting the exact same line-up as your opener, minus a shard and probably your profession procs. However, based on RNG for nightfall your actions will be limited.
Since you say you're "reacting" to your trinket procs you will be missing some of their uptime as Relic's proc time is 15s and DS is 20s. Their endings won't line up. Due to the nature of latency and non-robotic reactions of humans you will be missing a second or two of those procs after casting DS and your first DoT (or all 3 with SB:SS) Theoretically you could react in one GCD, but I'm standing in front of a target dummy, forcing myself to try and press DS and my SB:SS macro (on two different keys obviously) at the same time as I react to a proc, but I still end up doing two seperate key presses making it a little longer than 1 GCD. I imagine during an actual fight this would be even longer.
So based on this I'd say you should definitely start with a SB:SS+Haunt. This gets you right in to the money making zone and in to channeling MG as quickly as possible. Now after beginning to channel MG your Relic's proc will have 12-12.5 seconds left and DS should have about 18-19 seconds left. As you can see you're going to run in to an issue of whether or not to overwrite DoT's that have a 3027 intellect buff on them. I personally choose to go ahead and treat the relic proc as my #1 priority and will try to get fully Pandemic'd DoT's with Blessing of the Celestials (Relic proc's name).
Summary: DS, SB:SS, Haunt, MG 2-3 times, Hard-cast, MG, SB:SS based off of the timers as explained below. (3 shards used.) **Note**: No Haunt cast after hard-casting
Two cases arise here.
Case 1:Since we are treating this scenario based off of two procs I would recommend hard-casting as UA is about to expire and then SB:SSing right before BotC expires. DS will still have some time remaining, but I forego refreshing before it ends since I don't want to drop 3027 intellect on my DoTs.
Case 2: Personally I have Lightweave and Jade Spirit to account for as well. If we started this sequence with just Relic and Light of the Cosmos procced and neither of my other procs kicked in then I would follow the order from Case 1. Whats more likely is that Lw and/or JS procs during this time and those durations will extend until the end of my DS time. Together they are worth 3650 intellect and I'm willing to let Relic's proc drop and refresh my DoT's based on DS expiring. If only one of them pops up then I'll make a decision based on how frisky i'm feeling. We're talking about decisions made in fractions of a second during a fight so there really is no wrong answer as long as you aren't about to take an Annihilate to the face.
From here if RNG was nice to you you have acquired at least one nightfall proc you can cast Haunt after that final refresh and carry on until the next time DS is up. If RNG was a b*tch then you just channel MG and wallow in misery
Scenario 2: No DS, just trinket procs.
Easy. I'll refer you to Zagam's post HERE
and scroll down to the bit about Affliction's opener and soul shard management (or better yet read the whole thing if you havent done so already!).
Basically, hard-cast then Haunt. The only exception would be if you had 4 shards for some reason then go ahead and SB:SS, but the general rule of thumb is to hard-cast with 3 or less shards.
Scenario 3: Both trinkets just expired, DS just came off cooldown.
Dependent on a couple of things, but generally, don't wait. Pop DS.
I don't know your gear setup, but I'd say its best to use DS on cooldown to maximize the amount of time you can use it. Its a huge buff in and of itself so holding on to it isn't the best idea except in certain situations depending on what boss you are fighting.
Shard-management is very important and it sounds like you already have a pretty good understanding of what to do. What I wrote is purely a suggestion based on my personal playstyle so try to find what works for you!
Edited by Cruzan, 08 February 2013 - 08:01 AM.