Top 5 Five mans..

[Renisis86]

Murmur was the best

[Looq]

In no order

Shadowfang Keep(Classic)(First dungeon, love the style)
Well of Eternity(Awesome lore with Illidan)
CoT Stratholme(Love the waves of mobs,lore)
Violet Hold(Again, the constant pressure, love it)
Black Morass(^^^^^^)

[Wrathonia]

I actually miss all the old dungeons. For the most part I detest how they have been remade and streamlined. Strat is a bit better in this regard, but Scholo got ruined in the remake, I feel. I miss having 5 mans that made you get better as a player and actually have to talk to your party members to work out strategies. I miss having to fucking communicate. Most dungeons now-a-days are silent zergfests. I am happy if I can type 'Hello' before the tank pulls the first group.

[Zuben]

With the exception of WoE my list consists only of Vanilla and Wrath dungeons, as my touch with Cataclysm and MoP dungeons were too light to make a lasting impression(the increased difficulty turned me off from the former and the latter was defeated by LFR). TBC dungeons are not included as I didn't like the lore or aesthetics in any of them. Maybe Magister's Terrace, but not as much as with Classic & Wrath dungeons.

In no specific order:
- Classic Scarlet Monastery & Armory. The new ones are fine too, but the old ones I have fond memories of.
- Upper Blackrock Spire. At the time it felt like top end for me, and featured enemies like Rend Blackhand and even Nefarian made a guest appearance in his human form. Because it required a key back then I didn't get to run it as much as, say, Stratholme and Scholomance, so UBRS was left with a loom of mystery for me.
- Drak'tharon Keep. The Drakkari architecture felt grand compared to what we had seen of the Gurubashi and Amani style previously. Drak'tharon had that, but it also felt a little bit more lighthearted as it stood on the border to Grizzly Hills, which is one of my favorite zones in the game. There was that something in this dungeon. It also ended the Drakuru questchain in a surprisingly interesting way.
- Well of Eternity. The layout, mechanics, aesthetics and loregasm in this one are superb. I only did it once, but that was enough to fall in love.
- Pit of Saron. The layout, mechanics, lore and aesthetics made this one stand out the most of 3.3 dungeons. Halls of Reflection was awesome with us running away from Arthas as fast as we can, but otherwise the instance lacked the versatility Pit of Saron offered. I also like the voicework of Tyrannus, taunting us along the way.

[Okacz]

5) Classic Gnomeregan - it's like BRD, but done right. More a separate warzone than a instance, Gnomer had everything: a alliance-only arena with slot machines, funny punchcard feature, optional bosses, hidden patterns for engineers - and speaking of engineering, venturing into Gnomeregan with Gnomish Universal Remote is one of the most awesome things ever.
4) Scarlet Monastery - and I mean the new one. A completly different take on Scarlet Monastery instances, with trash being various and fun, Layout being less confusing, and with overall feeling that you are in a living place. Plus, a great reference to Rocky IV with the second boss.
3) Grim Batol (pre nerf) - some of my best pve experiances were in Cata, and Grim Batol was one of them. Each boss on heroic was a challange, where you coulnd't screw up even once or you're dead. Last boss being the quintessence of that, and I don't know if Erudax isn't my favourite 5 man end boss ever. Plus, the option to clean the trash with drakes. Want to have a smoother run? Well, work for it!
2) Stratholme - this place really wins when it comes to being climatic. Recent changes kinda took some of it away, but not all. The place where every moving thing wants you dead. The gates close behind you, Eyes of Naxxramas are vigilant, the trash is all over the place. Also, this place featured a LOT of things to do. Again, like old Gnomeregan - more a separate zone to explore than an instance.
1) Stonecore - I don't really know why this one is so high, but when I think about the best instance ever, this one comes to my mind nearly instantly. Everything seems perfectly balanced here. Trash is interesting and difficult, but there is not too much of it. The bosses require some knowledge, but are not too unforgiving. Millhouse Manastorm. I remember when I used to solo this place for some time to get the mount from the second boss - and even tho I ran the place several times in a row, it didn't get boring too much.