I am pretty new to the game, so take my views with a grain of salt :

I've tried HRE, Danes, French, and Spain for test runs when I first got the
game. I also gave the Egyptians, Alo's and Aragon for smaller tries. From
what I noticed, Spain seemed to be the easiest to get going, with the
Danes in second. France was also very easy if you rushed the English, but
that is what you have to do with the Danes too for the most part. My only
problem with Spain is that I don't fight too well yet with the Jinuettes (sp),
but I'm learning fast. They have great position, very good lands, tough units,
and usually several great generals...... what more could you ask for?

My favorite is still HRE for ancestrial reasons .