Please bear in mind that I've made my choice, and you can chose whatever you like, but consider this:
OPEN Servers have no bolstering in PvP areas. What does this mean exactly?
On a CORE server, when you enter a PvP zone, you get your rank temporarily raised to a predetermined rank (8 in teir 1, 18 in teir 2 etc). This is to enable ALL players participating in the RvR to be able to contribute in some way. It also means on a CORE server, you can effectively rank up via PvP only if you like. It'd be a bit slower, but more power to you.
Forget greifing by rank 30 players on rank 11 players. When you rank up to 11, and need to move to tier 2, you'll be competeing in open RvR against players much higher than you. Thats not even including the players from teir 3 coming back to act tough.
Also, if you group up with players more than about 4 ranks higher/lower than you everyone takes a big exp hit.
Unless your in a very large and highly organised guild, in order to participate in all this wonderful PvP you are all expecting, your going to be forced to PvE so much more just to be competitive in PvP. Sure, you can still PvP like crazy, but your going to rank up so slowly your just going to be falling further behind.
Morgrim - Ironclaw Server
Rank 40, Renown Rank 31
Immortal Guard Guild
Loaar - Retired
Galka, Pheonix, Serene LS
RDM 75 / PUP 75 / NIN 75