Hello Asper!

I don't know if there really is a 'best' clan, really. I enjoyed playing the Shimaza on my first go, but I have no real preferences here.

I did a quick search on the Era's package:
Total War: Eras includes every currently available Total War game: Shogun: Total War with the Mongol Invasion Expansion Pack, Medieval: Total War with the Viking Invasion Expansion Pack and Rome: Total War with both the Barbarian Invasion and Alexander packs. All of these outstanding products make up one of the most critically acclaimed and commercially successful PC real-time strategy franchises ever.

I believe it contains the latest versions of the games, so patched and all.

Hope that helps!