If your game time is limited and you want to avoid queues, you probably should reconsider rolling Horde. Since most PvP focused players rolled Horde for the racials, there is a huge surplus in Horde PvP’ers and they have queues for the BGs (WSG seems to be down to 5-10 minutes now but was around 20-30 minutes, AV is around 20-60 minutes queue) while Alliance has instant queues around the clock (except the 3-5min forced waiting time Blizzard added to prevent premades). Horde queues seems to have become a bit better, but that might change anytime again.
Besides that, some servers already have queues again and the 5-6 biggest servers had some serious issues when BWL was released with crashing world/BRM servers and people were unable to get into BWL for the first few days. That seems to be better now, but if you want to see unique events like the opening of the gates of AQ, you are most likely to see a queue window there or crashing servers/technincal problems when thousands of players try to get into Silithus. Unless you really have and want to play on one of the fullest realms, you might better skip those, queues and technical problems with every new phase are likely there. There are also several high servers which aren’t close to full or already have occasional queues.
Regarding challenge, I’m playing on the server with the second worse A/H ratio which survived P2 (Skullflame), even lately it seems to have shifted from 33/66 to 40/60. If you don’t mind playing on a medium server with a pop of around 3-3.5k (some consider it as “dead”, some enjoy playing on realms with a pop size the world was build for since Vanilla had a pop cap of 3k players, it really depends on your personel preference regarding pop size), you’ll find enough Horde there while the world is still playable since it’s not overpopulated.
But the best way to find the perfect server for you is to scout them, like you did, observe the chats and /w some random players and ask them about how they think about the server.
BUR