The easiest one I found was the lined patch pocket follow by the hip pocket ( high-end street) and the hardest one I found was the slash welt pocket ( couture), must say that I am absolutely adored this pocket because it gave an smart elegant look that you can popularly found this pocket in most of tailored suit.
I personally love tailored cut because it look elegant, sophistication and smart. Even though it is very difficult to do but I think it is worth it to challenge your self for a professional standard look.
Here is my slash welt pocket sample.