Very hard to answer, even with the information you gave. Speaking from my own perspective being a 100% pvp player (I don't even do HCs cause I dislike pve so much) I'd say that Lordaeron is a good choice if you like the idea of progression. I've played here for the last three months or so, and I really enjoy it. At the end of the day it all comes down to if you have people to play with, and if you enjoy playing with them - which I do. I always really enjoyed the progression of seasons on retail, and this is very well simulated here on Lord.
Blackrock speaks for itself I guess. It's a really nice server, and I used to play there a lot back when it was AT, but to me it came down to it being too repetitive. I liked the wotlk content, but doing it with virtually the same gear and meta-game for so long just got me sick of it. On Lord it's still wotlk, but the meta is very different.
Icecrown? Well... You will have really bad gear and everyone else will have really good gear. Can you handle that frustration until you're geared enough to play at a fair level? If so, go ahead - Icecrown is your choice.
If you do end up leaning towards Lord though, consider the fact that leveling will take you 5-7 days of /played time, depending on class and how much time you spend at the AH, in BGs etc during leveling.
If you, or anyone else for that matter, want more info specifically about pvp on Lordaeron from the perspective of someone that only plays pvp, feel free to respond here, or PM me.