I voted for EQ2. I've played both. The RP servers in EQ2 have good pops, so those are the places to play.
WoW is more casual friendly, but it lacks the complexity, depth, and epic feel of EQ2. Take a simple thing, like speaking another language. My 42 EQ2 monk can speak about a dozen, and when I switch to speaking the goblin tongue, anything in /say comes out in goblin. Players who haven't learned that language see a much of a gibberish. Its a small simple thing, but its there just the same.
EQ2 average age is around 20ish, from my experience. Compared to WoW 14 on the 'RP' Servers, 12 on the normal servers, and 10 on the PvP servers. Older, mature players are there, but you have to really dig to find them. In EQ2, they are right on the surface.
I know WoW has a trial, but the EQ2 trial may be going through some significant changes in the near future.
Edit - You'll get bored with WoW in about a month, once you realize that the game play is identical and you have grind to get good items in order to be effective in PvP. My own roommates run through the same instances as often as they can in a weekend trying to get certain pieces of armor or weapons. In EQ2, most of the best items come from various Heritage Quests.
And lastly, I hope you don't play on weekends, because its going to take you anywhere from 30min to an hour to actually log into WoW. The lag in WoW has been a problem since the game's release and they've never really eradicated it. Loot lag, in particular, is very annoying. When you loot, you click the item in the loot window, nothing wrong with that. But when it lags, and the item doesn't snap to your inventory, you have to wait until it does, or the item stays on the corpse. Try and run away from the corpse, and your character stays in the looting animation, and sort of skies along the ground. Its kinda funny the first time, actually, pisses you off every other time.
I started playing EQ2, moved to WoW when my EQ2 players got orders abroad, went back to EQ2 to see the changes, went back to WoW, remembered why I despised the game, then went back to EQ2 again.