My easiest character to write is Boromir from Lord of the Rings. I have a good feel for his character and how he speaks and responds, and I enjoy writing him and his interactions with people. I also have a couple of OCs that are easy to write. I used to have a hard time with Gandalf from LotR, but he's getting easier. The hard ones for me are women. For some reason, I struggle with writing women, which seems dumb, but there you go. ;-)