In my games, I tend to feel bad for the Karlings. No matter how hard Charlemagne works, his whole empire implodes because the franks are OBSESSED with Elective. I tend to avoid playing there just for the mess I've seen befall Karlings.
House of Cantábria annoys me. Ugly coat of arms looks like an unfinished job and I wish I could play a d'Astúrias noble instead. King Aurelio is a cool guy, innefective and old but nice and usually smart in picking his wars. His male successor, Veremondo is a shite person, murderous revoker and a tied with the worst of house Jimena on the kinslaying game. None of them, NONE of them pick their historical successor, Silo de Pravia, because the game gave him a county that is not dejure. Why? Beats me.
The Ummayads are a problem and I hate them until they are out of Hispania, than I bring just one back, convert him to Catholicism and give him some land because I love how their coat of arms look.
I feel the same for Charlie. Every time I play as him, it's always an independence faction or an elective faction that's the strongest. When I play as a vassal under him it's still the same, with the AI urging me to join their revolt. And of course no one likes it when he dies because of the border gore, and then the yellow blob from the south sweeps in, the rest is history.
Update: After playing some games at the 867 start, I got some new dynasties to not like:
de Cantabria - Playing as Navarre, trying to get my de jure lands back, these damn Goths just won't let go. I kinda want the Umayyads to ram them through at this point.
Welf - playing as the Anjou family, a German owns the duchy of Anjou, and prying it from his German hands took me way too long. In the end I massacred as many of them as I could.
Presmylid - Play as the Hungarian Arpads, settling, and the becoming Catholic. These damn Bohemians won't stop pushing their claims on their old lands, while I'm fighting a civil war. Go away please.
Karling - Karlings again because wacky inheritance laws make Europe's inner borders disgusting.