Rogue is a little more scattered. Assassination Rogue offers amazing single-target damage and a few key skills that really help support key party/raid members. Combat Rogue is slightly less interesting, though their increased AOE potential makes them an exceptional choice in specific encounters. Much like Destruction Warlock, Subtlety Rogue is a good option that is just notably worse than the alternatives available.
It’s hard to go wrong with Death Knight if you’re a melee DPS fan. As long as you’re willing to learn the class and level them up, you’ll love the sheer damage and power potential they offer out of the gate. I prefer the versatility and long-term damage potential of Unholy over Frost, but the choice between Unholy and Frost may come down to preferences. Blood can technically be a DPS contributor, though it’s best to treat them as a tank.
Mage finds itself spread across the DPS board. Arcane Mage is just an absolute damage-dealing machine that excels in both single-target and AOE situations. It’s just an insane overall DPS spec in the early days of the meta. Fire Mage is very good, but they don’t get going until later in the expansion. It’s a good idea to start “gearing” for a Fire Mage swap later on, but they’re a tougher sell at the start. As for Frost Mage…well, they’re still good in PvP and excel at quick leveling, but their potential caps out pretty quickly from there.
As is usually the case, Hunter is just a fantastic overall DPS option in WoTLK. Beastmaster Hunter does get better as the expansion goes on, but Survival and Marksmanship are exceptional DPS options from the start. Survival is the better option at the start of the expansion, but it’s arguably surpassed by Marksmanship towards the end of the expansion. In any case, Hunter excels in solo play and group PvE situations.
WoTLK is also the first WoW expansion that may have you seriously considering swapping to Shadow Priest. While they do suffer a bit as the expansion goes on (the same is true of some other caster classes), they’re an invaluable asset in early group content. They’re also a much better solo class than they have been in the past. Get some Shadow Priests going with a few great Warlock players, and you’ll be laughing at the surprising “ease” of a lot of early group content.
Enhancement Shamans are actually one of the biggest “winners” in the early days of the expansion. WoTLK was the first expansion to treat that spec as proper damage dealers rather than as a kind of hybrid class. There are technically better options, but Enhancement Shamans bring a lot to the party and can deal a ton of damage if used correctly. Elemental Shamans are…not as good. It’s hard to justify picking them over other caster options, though it is always nice to have Shamans in the party and they can pump damage from time to time. If you love playing as Elemental Shaman and your group is cool with your preferences, then you won’t feel the pain of playing one too often.