I think wotlk is better than tbc for a player like you, simply because it is said to be for more casual players.
As for specific realm I recomend Lordaeron, its slow leveling, but as someone has said above me, its magical. You get to experience more content, you will learn more about your class along the way and you won't have gold problems unlike in icecrown where you level too fast.
It doesn't have small player base, its of good size. Icecrown however, is packed and you have higher chances of finding *******s. Theres also the ammount of legendaries being used by every kind of player and gear requirements are high for max level content because so many players already have good gear mainly due to the cash shop, which are things you won't like.
Lordaeron has a bad side too, it doesn't have RDF (random dungeon finder), this doesn't bother me and it wouldn't bother you either but we just don't have enough players making groups for low level dungeons, but when a group is made you will probably make friends as vanilla dungeons require effort and your group will have to count on eachother to get through.
Dungeons, even tho require effort, are a good place to learn about your class, don't feel discouraged into joining one, join whenever you get the chance to try it out (questing makes you level up faster, dungeons gives good gear that gets replaced fast).
Icecrown has RDF and you can level up only with it, but your game experience will be incomplete, still, (depending on how many dungeons you do) you will reach max level with enough knowledge about your class anyway.
Lordaeron is said to have hardcore PvE content, but its only for some max level raids, where some bosses were buffed, but they're not as hard as you might think, at least at low dificulty settings, which will be enough to prepare you for harder dificulties. Even as a newb, these buffs won't keep you from raiding.
Lastly, Lordaeron PvP is present but not as much as in icecrown, players in lordaeron prefer to PvE but at least PvP is more balanced as its not "p2w" (most people won't "1-shot" you). PvPers usually prefer icecrown simply because it has more pvp in it. But for newbs, PvP in lordaeron is good enough.
gl hf.