Fav: Kings Fall
Least Fav: Spire of Stars

My favorite would be Crota's End. I guess because it was essentially a glorified Dungeon prototype (especially since we were 3-manning it by the end of D1), and Dungeons are my thing... but that mad dash through the darkness as an endless flood of enemies overwhelmed you is an experience that has remained unmatched in the Destiny experience.

Least favorite is a heck of a list to pick from, but the absolute worst would would be Garden of Salvation. It's far too unforgiving for individual mess-ups with no slack to adapt with, and the secrets and challenges are far too tedious. But at least it didn't have 500 symbols to memorize like Last Wish did. Ugh.
I think if you added my Garden of Salvation, Scourge, and Last Wish runs, you'd still be in the single digits (not counting the final boss farming we did helping folks get Anarchy before the sunset).

I don't think anything in Destiny has matched the OG Vault. Some stuff has come close...ish, but I've lost hope that the raid team at bungie is at all interested in pushing the envelope in the same way VoG did when it first launched. It feels like every raid since has just been tepid rehashes of the same (or inferior) mechanics.

Least favorite is probably King's Fall. It starts out really good and then just nose-dives into the opposite of fun town.

Favorite: Leviathan. I really liked how diverse it is.

Least favorite: King's Fall. Totems at the entrance of the Warpriest is in my top 3 favorite Raid encounters, but I really do feel very meh about boss rushes and boy does KF deliver that.

Scourge of the Past and Last Wish are 1A and 1B for me. Scourge is all-killer-no-filler, and Last Wish just has the most of the best encounters (and one I don't like).

Least is VoG, but I'm still happy to play it.

Honorable mention to Crown of Sorrow, which I have the fondest memories of for overcoming difficulties and truly mastering the final encounter.

I'm not a raider so I have minimal exposure. I've been carried through every one I've done.

Fav: Vault of Glass. Got my Vision of Confluence on first attempt not knowing it was a meta weapon (at the time). I just thought it was another Scout and thought it was pretty good. I was able to understand the tactics and complete the tasks without frustrating my teammates.

Worst: Kings Fall. First attempt, we played for 8 hours and still didn't complete it. The encounter where we have to fight that big Ogre with the bubble stalagmite things took us 5 hours. Our sherpa was trying to get the weekly challenge, and I didn't realize that. I just wanted to beat the thing. Tried the next day with a new Sherpa and beat the whole raid in 3 hours. 4 people in the group were first timers.

All the other raids, each encounter was over my head. I would just follow directions and not know why I was doing anything. Just tell me what to do and I'll shoot aliens along the way.

I love them all, really, even the raid lairs. Raiding is what makes Destiny special, IMHO.

There are some encounters I'm not a big fan of, but there's always at least one that I love in every raid. I hated the sisters in the original King's Fall, but the jumps are easier now, and I only freak out a little when I get taken. I think King's Fall and Leviathan are both too long.

Deep Stone Crypt is the best all around. Best aesthetic, and it has some of the best unexpected sequences of any raid.

Garden is probably my least favorite. It's unpredictable and unforgiving. You can sail through it without a problem one week and struggle the next with the same people. That said, I'll never forget the first time I ran for my life across that poppy field.

Bonus favorite encounters of each raid in order:

Atheon

Crossing the bridge

Oryx

Siege Engine

The Gauntlet

Breaking Argos' barrier (runner up: the holomap)

Repel the assault (pitching orbs at ships in space!)

Sparrow Race

Shiro Chi (runner up: the vault)

Fighting Gahlran's deceptions

Evade the Consecrated Mind (first encounter)

The Descent (chaos mode)

Defending the obelisks (runner up: exhibition when it goes well)

Such good times...

although I love Vault of Glass, my favorite would have to be Crota's End. Really if nothing else, the memories that have permanently lodged themselves into my brain. Nothing in the universe can ever top this moment. That music alone inspired me to be the best at my craft:swordbearing!

And there's another moment I always love—not gonna lie, I can't remember exactly who I shared this with, but I'm 90% sure it was with DBO. Doing the bridge encounter, most people were having trouble getting across in time to kill the Swordbearer Knight, and losing the only way to kill him. So the guy holding the bridge up on the far side in the middle had to continually sprint in a circle to keep the bridge up while avoiding the growing number of Sword Knights trying to kill him! Literally all I could hear was the constant WHOOSHING of swords, our middle guy(I think it was Funkmon, or Stabbim?) screaming and sobbing while literally running with his head cut off, and all of us laughing so hard we couldn't even do our jobs. I swear, I thought I was going to suffocate in real life from laughing so hard...

For Destiny 2 I'd definitely have to say Crown of Sorrow—even though the original Leviathan is real close. CoS nailed the whole Duality theme, and maintained it throughout the entire raid, but also kept it relatively short, so that it felt more like a Raid Lair instead.

As for least faves, it would have to be King's Fall. In my opinion, King's Fall is actually one of the best planned and most lore-perfect raids they've ever done. But what unfortunately knocks it to the bottom is the absolute rigidity in making the mechanics work. Not only do all six of you have to be perfect, but all six of your internet connections have to be perfect, too—otherwise you'll be in a constant state of wipes, even if everyone is doing their job and doing it right. Speaking of, in most cases even one death can be enough to tear a whole attempt apart, depending on the job, or again, the internet connection. And when it's not even your fault, you want to play less and less. I guarantee you at least 20% of my accumulated time in Destiny 1 was waiting for someone to answer an LFG in the final area. Not fun.

In D2, I'd have to agree with whoever said Garden of Salvation. None of that raid is fun to me. I've only played it twice in my life, and one of those was for Divinity. ALSO not fun. But even so, it has to tie with Spire of Stars. THAT junk was such a mess I ended up accidentally completing a full catalyst for Rat King—0 to 100—just on retries alone. Nope.