I'm glad you asked, here is the breakdown:
PvE realm - less populated, but actually much closer to blizzlike feeling in terms of that part. No ganking and stuff like that. You can quest in peace and none can attack you from opposing faction.
BUT... i gotta state this as pvper, you really miss out on huge aspect of this game and it's called "open world pvp". Yes, there is ganking and corpse camping but that's what you get in war between factions

PvP realm - huge, ginormous population which has it's pros and cons. Cons being that certain profesions are damn hard to level cuz of resource scarcity and lagg spikes which occur randomly (but not every day). You can also be attacked on sigt at, literally, any moment due to huge number of opposing faction players in same zone as you.
Pros being - feeling which you won't get on any other game. It's very nice feeling to actually share the world with people in it and not sit in damn hub pressing hotkeys to queue for stuff. It's very nice feeling to be able to get questing groups so easy, dungeon runs (some dungs are still hard to get running tough)...
It's great feeling to gather few guys and actually kill that high lvl ganking bastards. I gathered entire Tarren Mill and we killed some 60 lock , Mortadela

Was epic feeling to sap him 3 times and see others preparing to swarm him

If you pick PvE you will have nice smooth time without interupting your leveling.
If you pick PvP you will have amazing stories to tell and much time spent cursing them gankers.
I picked PvP... just makes game feel right. You aren't missing that lore part of war between two factions.
Whatever you pick, good luck and have fun !