tbc is the 2nd wow expansion, followed by wrath of the lich king(wotlk), then cataclysm (which warmane doesn't support anymore) and then mists of pandaria(mop).
both tbc and wotlk are well scripted, mop lags behind but is suppose to be getting some work done. i'd suggest going with either tbc or wotlk solely due to more things working on them. i'd go with downloading both tbc and wotlk(old) and trying them both, then see which you like better. wotlk has 3 realms, lordaraon is 1x xp with some buffed content (meaning it's harder than normal) icecrown is 7x xp, not sure if any content is buffed. and blackrock is instant 80 pure pvp realm, so no quests, dungeons, or anything of the sort. for icecrown you may run into the login queue depending on when you play. if it's an issue you can either donate once and skip the que, or you can play on lordaron, it's not as popular as icecrown but still holds a good population.