Hardest Faction

[Martok]

In XL, the small factions (with the exception of Danes, Venetians, Sicilians and Genoese) are pretty hard to play. I remember playing as Portuguese on early. Spanish and Almohad ganged up on me and I died. The starting king isn't that influential so it's hard for the player to secure its position.

Whether XL or original I find playing as HRE pretty easy on normal setting. It's just pretty much the western version of Byzantine. I find playing Poland or Aragonese more difficult.

Yeah, Portugal is tough in the XL mod--although to be fair, all three Iberian Catholics factions are pretty difficult (the Spanish were pretty easy in VI, but they're much more challenging again in XL). I'm considering giving Aragon another crack, though; southern France is awfully tempting when the French get ex-commed.

I would rate the HRE as "fairly hard". They're not as difficult as the Polish or Aragonese, but you still get hit from all sides, and are always getting ex-commed by Rome since you're usually at war with one or more Catholic factions.

The Danes aren't too bad, as long as you expand quickly and don't turtle! Grab Scandanavia as soon as possible, of course, and then from there you have 3 main options:
1.) Send your armies east, and make the Baltic Sea your own personal mill pond. You can usually establish a strong northern kingdom this way in relatively short order.
2.) Given how they tend to be at war with multiple factions and/or excommunicated all the time, the Imperial provinces of northern Germany tend to be easy pickings, especially since their garrisons are often stripped of men to reinforce the Empire's armies on other fronts.
3.) Conquering England--although I've discovered this can be awfully risky. While they have pretty decent lands and are worth taking, I find I have to invade in large numbers, even if the island is lightly defended. The English people are surprisingly frisky, and require significant occupation forces if they're to be kept from rebelling.

[Samurai Waki]

hmmm....Elmo's can be hard, especially in High and Late. Also Byz in High and Late. I really haven't played a full campaign as HRE so I can't say much for them. My hardest Campaign was probably my Turkish Campaign, I started in Early, kicked the hell out of the Byzantines, and was well on my way to conquering egypt, then came the crusades, and just utterly wrecked me for like 100 years, started a civil war. Yeah Big Bloody Mess.
Then the mid 1300s came around, and I got my Janissaries, regained all of my lost territory and then some. In the end I won a minor victory, but I was happy all the same, toughest campaigns tend to be the most rewarding in the end.

[KrooK]

I think tourkey is easy into campaing but hard using single games.
I played turkey and I noticed that one jihad cost only 500. So when i played i was conquering prowince and withdrawin from it. Computers reconqueredit and then i couldsend jihads. Not one or 2 but usually 6 :) My army was soon undefeated and I was waiting on crusades :)