The Ages

[Lazy_Perfectionist]

Middle age isn't bad.

With late age, you'll have to deal with Ermor, Ashen Empire.
With late age, you'll have to deal with R'lyeh, Dreamlands.

I say start with middle age because thats where I got my multiplayer experience in, not for any real reason. But with late age, you have some very dominion dependent nations you might encounter that'll mix things up.

In middle age, troops tend to be more diversified as well, which will give you some additional flexibility. For instance, EA Ctis has zero scouts. MA has them.

What is the most interesting? No opinion yet, I'm not 'experienced'.