During the last four levels of my shadow priest Pupunen I got my experience mainly from questing. That's what I started to do with the toon in the first place and I decided that that would be the way she would become of age.
However, the lure of the LFD was too much for me, so I gave in a couple of times. Most notably the last Culling of Stratholme, when Pupunen dinged the final ding in this expansion. After which she moved on directly to heroics.
And that was the moment I made the horrible discovery.
PUG in levelling is more horrible in all aspects than PUG in level cap.
Really, the levelling PUGs are a cesspool of badly behaving primadonnas trying to shine with their level capped, Lich King slaughtering mains. Most of the time I felt sick with the bragging and/or bad playing in there. The worst ones were the runs where the tank stated that he was in the instance first time ever and got laughed at. In the end, the dps DK laughing called some names and left the group due to 'noob tank' and 'healer suxx'. (Sidenote here: it was for the best of the run. The replacement DK was excellent professional, who told the group after the instance that it was his first time there, too.)
Then I hit the cap and switched directly to heroics. What a bliss! Smooth runs, no-one was evaluating you and as ranged dps everything was luxury: keep the dps up, always keep casting and stay out of goo. It's way much easier than playing a tank, really. And even more easier than playing a healer!
There is nothing to tell the other players that you are screwing your rotations. Other than dps meter, which everyone is trying to avoid not to show how they are slacking, too.
Playing a tank or a healer is much more straining, that is for sure, and I had had my thoughts on how much easier playing a ranged dps is compared to those positions.
Now I know.
But I also know that the levelling PUGs are awful when compared to heroics at the cap. I don't think it's the water of Northrend that makes the levelling PUG players so bad: it's the air of most exp in least time which these games have taught us to min-max.
It's the idea of playing the game instead of playing a RPG and enjoying the ride.