you will be able to talk with people in ACII. In AC III you will have more fellow passengers but that class is crowded and you may not feel comfortable. AC I is quite luxurious where you will get a lot of 'privacy'
If you want to feel the environment of the places train is passing through, you should go with sleeper class(non-ac) but this class is crowded with so many beggars, vendors which are most of the times disturbing.