depends on what you are interested in...
pls elaborate.
well idk I've never played the singleplayer so I dont know what to expect. I guess the mod with the best content.
Floris if you want a far better version of the native singleplayer campaign. 1257 AD if you want a fantastic mod set in medieval Europe. Prophesy of Pendor if you want a great fantasy mod with a well written story and good characters/factions/events. Brytenwalda is also a really good mod set in the British Isles during the viking age.
Those are all some of my favorite singleplayer ones, I'm sure there are others that I missed.
Brytenwalda was not set during the viking age... It was set during the early Dark Ages, before Alfred the Great took control of first united England... The Vikings were only getting started at these times, im talking around 450 A.D that Brytenwalda was aimed at, only 40 years after the Romans left. The Vikings never really started coming to Europe until when Alfred the Great was around in the mid ninth century.
anyway, back on topic, if you want one set during feudal Japan, then Gekokujo is the way to go