Basically any castle/town with a narrow ladder or ramp leading up.
There are some castles/towns with unique layouts that are supposed to have chokepoints and towers inside, away from the initial ramp and troops spawn far away from the initial ramp. I don't like defending those places because once enemies get past the initial ramp, their archers can spread out and it is just too hard to keep alive then.
Believe it or not, I also don't like defending places that require siege towers. It seems the AI takes the same time from initial siege to attack regardless if they need to build a siege tower or not. And when they do build a siege tower, their archers have more time to shoot and kill your troops, especially your own exposed archers. I can't afford a battle of attrition, so I either have to pull back my own archers, which is hard, or just wait it out.