I liked 4 more than 3. I found 3 to be especially slow and I hated the miasma gimmick in the second half. 4 has a creepy hospital and probably the most complicated story of the series that requires more piecing together info from the notes you find, though that might have been the slightly wonky translation patch. Also remember it being easier than the first three due to an auto lock on mechanic, which may have been because the game required you to use the wii-mote and nunchuck. Not the most fluid way to swing the Camera Obscura around.
Probably rank them 2, 1, 4, 3, 5