Wailing caverns , but as for actual end content.. it was prolly MC or UBRS, dont remember which
Kara, on my warlock.
I'm pretty new player started in Feb '12. First raid instance I ever entered was TK at level 85 (with crap gear), watched some vids how to solo it and got pwned hard by kaelthas. First actual content raid - DS at 15% nerf, got up to Hagara with really bad pug that wiped even on normal morchok.
Still this didn't stopped me from rising to top 5% progress playerbase, finished MV before HOF opened, finished DS HC before 5.04 dropped etc. The only thing that I miss out on are some vanity feats of strength, don't care bout them anyway.
I was really really bad at that time.
It was either KZ or MH, I can't remember.
First time in MH was soooo epic
Blue text indicates sarcasm or joking.
UBRS, I got my Wildheart Vest that run and was stoked. Blues were awesome back then, and my entire goal in WoW back in those days was to complete the Wildheart set.
Baradin Hold to be precise, but not counting such not-really-raids it's BWD
My first raid was BWD. We were on Maloriak and I was tasked with interrupting Arcane Storm... being a first time raider and not having DBM it didn't turn out too good.
I'm a late BC child but I didn't know about real raiding till wrath and my first raid then was naxx. Sadly to say I was carried since I was reeeeeal shitty back then...
I don't really count getting attuned to MC etc being a real raid. I actually jumped straight into MC before doing the scholo/ubrs raids after hitting 60 because MC was just released and the guild needed healers.
So my first raid would be MC, the queue time was 2 hours on Dragonmaw EU, then it took another hour to even get inside the entrance because Blackrock Mountain was a real gank/Lagfest with all horde and alliance guilds inside 1 mountain. With the PCs back then you always died running straight off the cliff and with the lava not loading properly you could enjoy a nice corsperun. Fellow priests with a proper PC were mindcontrolling ppl and running them into the lava themselves.
When inside I found myself standing beside 5/6 mages conjuring water which they had been conjuring for the past hour, saw them conjure 3 times and then drinking up wasting 1/6 water they just made and starting over. Didn't think anything of it at the time but that must've been a real pain in the ass to do that every single raid. (Not to mention if they would ever disconnect after creating a lot of water and not being back in time for it to disappear....) For me, only the costs of the candles to buff hurt my very weak amount of gold.
My job was to keep powerword:Shield (and renew) on the tank at all times ! (lol). We failed miserably on Lucifron during this first raid which was actually the first raid for everyone in the guild. During the ~7th try I disconnected only to find myself in a one hour queue again. All in all if felt really really good even though you were wiping all night and trying to reconnect and beat the laggy shitfps etc. That imp cave felt really scary.
I can't really remember it that well but I think we had a healerrotation even for lucifron, maybe though I'm mistaken with another boss, was real fun to hear the call HEALER GROUP 2 ! and start healing, felt like now it was your time to shine when the call came. (And when they called another group you really liked just wanding and looking at wtf everyone else was doing)