A nice economical lens if that is what you need and at this focal length. Naglers and Panoptics offer less value or bang per buck and are for those, like me, who feel they must have them. However, my position does not always make good economic sense.
The 7mm is a 10, the 9mm is closer to an 8.5 and the 5mm is a 9 minus. The clear winner here is the 7mm. I wound up not liking the 9mm. The 5 is O.K., but I eventually went to a Pentax 5.2 XL instead and liked it better.