To answer the latter half of your question about difficult-to-write scenes, I’ll pick suspenseful scenes only because I haven’t attempted one yet, and therefore have no idea whether I’ll find it difficult to attempt or not. I imagine that a suspense novel may need some careful crafting and so will be difficult to execute on the whole. Each scene will have to be tight and fast-paced and yet descriptive and emotional, moving the story forward. A suspense novel has a lot going on within its pages, and its scenes will have to reflect that.
As for the easy scenes…I find that when I know my novel and its characters well, the scenes practically write themselves. But if I’m unsure of plot or where the story should go, that’s when I hit the road bump. It doesn’t matter what kind of scene it is—funny, sad, sexy, angst-filled—I have to know “what happens next” in the story and to my characters.
On the whole, I’d say that any scene, emotional or action-packed, is doable if I know my character and his or her story.