I'll go first! I put down T&M, for a number of reasons.
As a Man, I've always felt that the world revolved around Bree. I started my LOTROing there; thereabouts, anyway, and I saved entering the town itself for when I reached that once-high cap of level 15. Did I wait for the game to go live? Maybe; it was close.
For the longest time, Bree was the hub of all adventures. Even when I journeyed across the North Downs and beyond, it was at Bree that we met up for the Rift or a port to Carn Dum. Even when I first laid eyes on Rivendell, it was never a place I was pinned down to, just a place to go through to reach points beyond. It was like I was a rubber band, nailed down at Bree, stretched to Rivendell and just looped around up there, for a little relief, and then I made a deeper plunge into the heights of the Misty Mountains and down into Goblin-town. But when the journey was done—sproing!—I'd let go, relax and zip back to Bree, back to HQ.
And now these bastidges are taking it over?!

This will not stand!
A proto-version of T&M was the inaugural Skirmish where we whacked on Bill Ferny a bit. Because of that, because of that prototypical moment, I have it in my soul as T&M meaning the Basic Skirmish, and that, in a way, everything was just a modification of that. Like how the Model T is
the car and a Lambourghini is just a few tweaks made to the concept.
Also, at the beginning, T&M was the only offensive Skirmish, and as a crazy and aggressive Champ, I like being on the offense. >D Also, this means that I can take a break if I need to, go get some dinner or something, take a bio break, whatever. And, because of
that, it meant that the Encounters were full-blown Elites. At last, a real challenge! (Of course, most of the end-game Skirms in the epics are offensive, but how could I have known that?)
Lastly is T&M's "Capstone" feel to it. Everyone with us that fateful day can attest to haw crazy hard Raid-sized T&M can become. Likewise even as a Fellowship. There was more than one night of cruising through six-mans with ease and then stumbling a bit on T&M. The place stands there, all smug-like, saying "Yeah, it's a challenge, it's not a gimme. How 'bout that, huh?" Doable, sure. It's not like we're talking Dark Delving hard or anything. But it's still something that smacks you in the face and makes you say, "Oh, crap! They're not just bags of HP to kill!"
But Thangulhad is the best for SM. :3