I would just join the highest-ranked auto-join guild. People are usually active in those, and you can never go wrong with a couple of fp's in your town hall. If you plan on guild hopping for a couple hours, join an older world where you can aid around 2000 people in one night. If you don't want to guild hop, then join a newer world like Angkor. Obviously, when you guild hop, you should avoid joining that highest-ranked auto-join guild until the very end, and then don't leave their guild.