Since the OP looks for 'beginner's server, mir2 & 3, I assume he wants a mir that is simple to play, without the many new features some servers have.
IMO that disqualifies mir3 because of its air/fire/earth etc elements that you can and need to add to your items. Mir2 is still with us because it is as simple as can be, you bash the monsters to get exp points to level... period. Many mir2 servers expanded to be somewhat like mir3, with added features that make the gameplay more complex but you can mostly ignore it, at least when starting out on the server.
I'd say, log on one server at a time, spend one evening on it, next day try another. Don't focus on the high user count servers only, often you find the smaller servers may just fit your bill. And being new to mir, since you say beginner, I don't think you need to select the server based on its potential staying power. Those several month lasting and smaller servers can be more fun than those big, established ones.
Try Nexus server for no-nonsense high rate leveling fest.