SKX007J is the so-called "Japan version" (supposedly made in Japan).
SKX007K is the "Singapore version" (supposedly made in Singapore).
SKX173 is a N. American model marketed only in, well, N. America, while the SKX007's are Asian models.
There have been some debates about whether the SKX007J is actually made in Japan and whether the SKX007K is actually made in Singapore, etc. -- the bottom line is they are models labelled differently for marketing purposes.
All the Seiko divers are very well-made and at less than $160 USD or so are a great value. It all depends on which style you like. They're all great divers.
Check the Seiko Divers Reference for more details:
Have fun with your Seikos!