Played Mage in vanilla up to Naxx (switched to Druid for healing then). Mages are top tier as everyone mentioned. Early on farming on a lock is way faster, once you get geared nothing beats mage aoe farm.
Mana being a thing was annoying as a mage, always looked on in envy as I had to wand and regen while locks just lifetapped (provided you had smart healers that did not oom). 1v1 pvp locks dominate mages too unless you get very lucky or outgear them.
That being said, mage was super fun and once geared was devastating. Top alliance premade would always have flag carrier carry a set of fire resist gear vs us, since me and the other mage could one shot anyone with trinket, pom pyro.
Both specs are pretty basic to play in raiding, xxxbolt spam (warlocks can’t go affliction in classic raids due to debuff limit)