I don't benchmark or track bugs, but, based on my own personal user-experience "feeling", 4.4.4's performance is better and it has less problems than 4.4.2 and 4.4.3.
Just upgrade no problems at all for me but since I recently bought the nexus 5 I can't tell you about improvements or compare 4.4.2 to 4.4.3 and 4.4.4 is just a security update as I read before