Tbh, I think we'll also have to keep in mind blizz's recent idea of 'challenging'. In concept, they almost sound like raid training (ei don't stand in the fire). I have a feeling like most things, they'll be 'challenging' when you're still wearing quest blues at 90, then as soon as you've geared up from heroic dungeons/LFR scenarios you'll be able to clear them like any 5 person quest mob.
Right now, I still feel the word 'challenging' as Blizzard uses it refers to the skill level of people who've played Farmville for the past 3 years as their main pastime.
Then again, with the introduction of Pandarens, I believe the sales goal is to attract a lower age group as well, since most of the Vanilla/BC crowd are in their mid 20s/early 30s now.
So... overall, I'd figure almost anyone would do well, but DPS in general should perform well, as the whole point of scenarios is to provide content for the ridiculous numbers of DPS in instance queues.
My guess is if you know how to play a shadowpriest... by the time you're half geared in LFR you'll be able to solo/2 man any scenario though.
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