For me it would be (and it was as I had the 5455 at one time) the 4155. I wanted the smaller form factor. Sleeves were not something I needed or wanted. I did not need or want the fingerprint scanner. Lastly, one of the issues that seems to have carried over from the 5455 I did not want to deal with, namely possibly having to remove the battery to fix a WiFi problem.
If they were both the same price or even if the 5555 was cheaper, I would still buy the 4155.
It is, however, a personal choice based upon individual needs. For some, their opinion would be completely opposite of mine.
-JmE-