One thing you gotta take into consideration when looking at classes for Classic are the things most people don’t bring up, such as:
Healers/Caster DPS:
If you want to play one of these, be prepared to have up to 4-6 different ranks of the same spell on your bar, and be able to know when is the best time to use a specific rank of a spell or heal. Mana conservation was a nightmare back then, and if you used your max rank spells all the time, especially in a raid, you’d be oom before the boss dropped below 90%. Mana management is the name of the game here.
Luckily there are some ways in which you can deal with it. Innervate for Druids for one restored a % of mana, as well as a mages Evocation, though if I remember correctly I don’t think either of those, or at least Evocation, could be used while in combat.
Tank/Melee DPS
Don’t think about rolling a Druid for example because they can be any role. Bear form might be fine for 5-man dungeons while leveling, but end-game tanking was the realm of the Warrior. Good luck mitigating a crushing blow if you don’t have a shield and subsequent Shield Block ability to go with it.
If a Warrior is what you’re after, keep in mind you’ll be losing a lot of your key weapon upgrades to ninja-looting, Rogues, and Hunters. Playing a Fury Warrior? Well the Rogue needs the 1-hander more than you do. Playing an Arms Warrior? Sorry buddy, but that two-handed strength sword would compliment the Hunter nicely.
Likewise, if you are a Hunter, expect to lose a lot of your ranged weapon upgrades to Rogues and Warriors. A bow finally dropped after three months of farming? Sorry pal, the Rogue needs the boost in stats more than you do. A gun that would boost your DPS significantly happened to drop? Well, we’d better give it to the Warrior so he has something to pull with.
And don’t even get me started on Paladins. Weak damage as Ret, sub-standard healing as Holy, and just a “meh” Protection spec means that the only real reason why you were invited to the raid in the first place was because your buffs were the only good thing about you.
Of course, two-handed Enhancement Shamans tore things up back then with Windfury being able to proc additional Windfuries off of Windfury procs. A lot of the time your auto-attack would one shot someone in PvP. Of course, the patch version they are launching Classic with I believe is a patch after that was nerfed.
Balance and Diversity:
Some classes were horribly imbalanced in comparison to others, but that also made each class feel unique and diverse. For example, a Hunters and Mages kit seemed like it was tailor-made to counter Warriors, with all of their abilities to keep you at a distance and slowed. However, if said Warrior did manage to catch you, that was usually GG.
Rogues had to almost wholly rely on their stuns and other CC effects because their armor basically equated to them running around wearing wet paper towels for protection, so if they weren’t good enough to keep you perma-CC’d then you’d rip through them in a heartbeat.
Druids being able to HoT themselves up then turtle inside Bear Form was just as annoying back then as it is today, maybe even more so.
Conclusion:
Each class had it’s strengths and weaknesses. Some were weak against certain classes or encounters, while others were stronger. I’d watch some old school vanilla class videos to get an idea of how they played, but I recommend not picking a class based off the videos you watch being as how those people were typically the best of the best for their server, and were able to consistently play their classes to perfection.
Sorry this is so long, didn’t expect it to be. I hope it helps however.