With Classic being limited to 3 battlegrounds if you're interested in PVP and especially getting to rank 14 you will visit these battleground a LOT.
So which one will be your personal favorite pick?
1. Warsong Gulch (10vs10)
The basic capture the flag game mode has no time limit in classic. Therefore matches can go on for quite a while if you encounter a strong team on the other side. Other than that there is not much else to say. People know the map and mode from the current version of WoW. There haven't been that many changes in there.
2. Arathi Basin (15v15)
Domination is the name of the game here. Hold up to 5 points on the map the gather 2000 resources before the enemy faction. This map is always on a timer because the resources will go up. The basic principle of this map should be known as this is well is mostly unchanged on live servers.
3. Alterac Valley (40v40)
This is a tricky one because we won't actually get the first version of AV. This BG had a major re-work in Vanilla already because it was pretty much dead after the release of the honor system. I remember that on my first server in version 1 of AV we actually had to schedule a session of AV because no one from the smaller faction on the server would usually sign up for it. Anyway the change of AV removed a lot of NPCs on the map and allowed for much quicker matches which in fact created the basic tactic of just ignoring the enemy players and just try to get a quick kill of the boss at the end. Sometimes big battles still happened if one faction went for a proper defense but it was rare.
The question is what will be your preferred bg?
Btw. option 4 refers to open WORLD PVP