I wish I could help ya, but I know very little about European WoW servers, having played only on North American ones.
I hear it can be pretty harsh on some European realms given the number of spoken languages all around... But I think it's safe enough to assume that there are plenty of English-speaking realms. I've just had an unfortunate experience in my first year of WoW (back in vanilla =p) when my main server turned from a fairly diverse mostly English-speaking server to the unofficial Brazilian server - and when more then half of your server speaks languages you don't (Well, I've got a grasp on very basic Spanish, but that's about it) it really is a pain in the ass.
Although given the cross-server grouping, it might not be such a big problem, at least until it comes to looking for a guild.
You should probably go to WoW European Forums to find which servers fit you better in terms of languages (really, I don't know how it works, but I assume there would be some kind of groups of mainly English-speaking servers, mainly French-speaking servers, Spanish, and so on) and the timezone. Then check over [link]http://www.warcraftrealms.com/census.php/[/link].
I don't know if it's very correct, but it provides a general idea on server populations and imbalances. Because some servers, even today, might have something like 1000 Horde and 12000 Alliance, or vice versa, and it changes a lot of thing. The Auction house is rather bad for the side with very very few players, grouping and guilding might be a problem and so on.
As for server types, I've generally stuck to PvP servers until about 2 years ago when I made the transition to an RP-PvP server. Frankly, I like it. RP in WoW is sadly mostly gone for various reasons, but RP-PvP servers seem to attract at least some of the more mature and interesting players to hang around with. All my best guild experiences come from an RP-PvP server.
And it generally allows you the flexibility if you do want to roleplay at some point. Although about 90% of the population, in my experience, doesn't give a shit. But at least there might be a few % of people less annoying then your average PvP ego-head.
Hope that loooooong rant helped.
P.S. And you can make characters on both factions of the same server even on PvP realms now. It generally helps, after you get to level 80 you'll have access to "Bind on account" items that can be a major help in leveling new characters. You can't send 'em cross realm, but you can send 'em cross faction... So after getting to 80 on one side and playing for a while, you can send out a set of BoA leveling gear (that levels with you and is generally better then most drops until high 70s outside of raids and heroics, and certainly less troublesome) which would provide you with up to 25% extra experience and a decent weapon that levels with you.
