I'm going to go completely against the grain here, but my personal favourite is RE5. Although REmake was fantastic as well.
RE4 was great, but was far too long. It started to really drag towards the end. RE5 refines the gameplay to perfection, imo, and is just the right length. I haven't got too far in RE6 yet, but I'm not particularly impressed with it so far. Too many QTEs.