Who drank from the well?

Well, my elven mage, Revas, drank from the Well - given the motivation of being in a position to help the Dalish by answering so many questions that have been left lingering for centuries (no matter the personal cost, and there was no romantic partner to dissuade him). As for your last question, was that meant to indicate who supported Abelas' position that no one should drink from the Well? Revas was able to mollify Abelas by performing the ancient rituals, so I was a bit unclear as to what you meant.

General rule I follow is that if I'm using a World State where Kieran exists, Inquisitor drinks, and if he doesn't, Morrigan drinks.
I do rather like the "Mythal Guardian" result than the "Morridragan" result, but on the whole it's harder to justify the Inquisitor drinking, for me.

I pretty much always do the ceremony and side with the Elves, though.  I did the tunnel once just to see it, but most of my Quizzies are respectful, curious sorts.

I have canon PTs with both, as it seems to be a pretty important decision. And in those canon runs I also always side with the elves.

In my first PT though, the game pretty blatantly spells out there'll be consequences for whomever drinks from it, so... I wanted a guinea pig. Yeah, Morrigan... have at it.

I've had both my Inquisitor and Morrigan drink in different playthroughs, but for my canon I chose to have my Inquisitor do it. Being Dalish she was not going to let an unknown, unpredictable person like Morrigan have that kind of (elven) power. Plus, I personally love how it complicates things even further with the whole Solas-Mythal thing, especially in a Solavellan playthrough.

My non-Dalish Inquisitors have never drunk themselves though.

I did the rituals, although I had to come to the forums to find out how to do one of them successfully: the one where you actually cheat by climbing onto the central raised area in order to avoid backtracking (how was I to know you could only do it by cheating?). Then I respected the decision of Abelas. When we finally got there I had the arcane knowledge perk that was telling me why it was not a good idea to drink. Cole told me it was not a good idea to drink. Solas told me he did not want to drink, plus when he first entered the area he exclaimed "So Mythal endures" (I think those were the words) that made me wonder if she wasn't as dead as was claimed. Nor did I want Morrigan to drink because I just didn't trust her seeing as it was clear she had been withholding information until forced to reveal it. It was also clear from some of the lore reveals that our Dalish idea of the Creators as benign teachers and guides might not actually be the truth. If the gods had murdered Mythal, then may be having their magic around in the world might not be a good thing. There had been no suggestion of needing the Well to defeat Corypheus before going to the Arbor Wilds. Still, why couldn't Abelas drink?

Anyway, it turned out that letting Abelas destroy the Well or drink from it was not an option, so reluctantly I usually let Morrigan drink because if the Inquisitor drinks and they become incapable of independent action as a result, then we would be well a truly screwed. I have to assume that Morrigan would at least use the knowledge to defeat Corypheus as he is a threat to her (and Kieran if alive) and just have to hope that she will oppose Solas in the future (unless of course he controls her).

So I voted for supporting the ancient elves but then letting Morrigan drink.

Only let Morrigan drink from it once to see what would happen, did it myself all the other times.

I`ve playthroughs with both the decisions but in my canon playthrough Morrigan drank from the well and my inquisitor performed the rituals and sided with the ancient elves.

I was totally down with being the god like ladies bitch, since the first time I saw her in DA:O, I thought, this crazy old lady is badass! And she only got better with time, but now... now I'm not so sure she'll hold the reigns.

I hope Flem lives.

Depends on my PC. In my first game, an female elf rogue romancing Solas, Morrigan drank. In subsequent games, Morrigan drank unless my PC was an elven mage.

Did the rituals and sided with the sentinels in all but 1 game, and that was mostly just to see how it differed. Considering it takes just as long, if not longer, to fight your way through than to do the rituals, I always do them now. Makes for a nice no-combat break.

I did the rituals and then let Morrigan drink from the well. No way, my inquis become slaves of a god - even if it's their own god.

My main is a Dalish Mage. She Drank from the WoS.  She's not too worried about being bound to Mythal considering she was sporting Mythal Vallaslin already (though to be fair she is a Solas LI, so she had them removed).   Pretty much boiled down to a combination of it being her heritage, her being more than knowledgeable enough about the topic (not as much as Morrigan, but sufficiently), and her not liking just how obsessive Morrigan was about drinking from it.  

Also, spite ... that was also a large part of it.  Even if it was due to shortsightedness on Bioware's part, you don't get to talk down to my Dalish Mage about her own Religion (and God she has magically stapled to her face) for an entire mission (with only older versions of the same mis-remembered theology the Dalish already have I might add), disobey a direct order to not engage with the Ancient Elvhen in the Temple, and say "Haven't I earned your trust?" when you've done absolutely nothing to earn it yet, and expect to get the power from the WoS by default.  Nope, sorry Exposition Mom, its not for you.  

If you can afford to, bring Dorian with you as well.  While his dialogue in regards to the WoS choice isn't something to write home about (its effectively, No I don't want it), he does have some really meaty optional dialogue when talking to Abelas in regards to the fall of the Ancient Elvhen Empire.  My party ended up being PC (Mage), Dorian, Solas, and Blackwall (because unlike Cassandra he is at least respectful about what he sees in the Temple).  Seriously wth Cassy?  It may not be as noticeable if you play a non-Dalish, but man if you bring her into the Temple of Mythal with you every other line is her insulting your PC's heritage and faith right to their face.