I get asked all of the time to comment on different cameras and to give recommendations. The latest question is, "Why would I buy a Pentax K-3 when Nikon just announced the D5300, which is similar but for $500 less?"
Initially the Pentax K-3 and the D5300 look like pretty much the same camera. After all, they share the same Sony-made 24 megapixel APS-C sized sensor and neither have an anti-aliasing filter. So is there anything that would justify the higher price of the K-3?
First, the K-3 is weather sealed and the D5300 is not. Depending on where you photograph, this could be a big deal. Having a weather sealed camera can be the difference between getting "the shot" or not.
Another difference is that the K-3 has a pentaprism viewfinder while the D5300 has a pentamirror viewfinder. Pentaprism is brighter with better coverage.
The K-3 has a slightly better auto-focus system than the D5300. The K-3 is overall slightly quicker.
The K-3 has two memory card slots and menu/button features that will appeal more to the professional, while the D5300 is aimed more at the mid-level amateur.
Finally, and this will have to wait to be proven, but Pentax has a reputation of getting just a little more out of the Sony sensors than Nikon. The differences won't be noticeable in practical purposes, but I suspect that the K-3 will have an ever-so-slight edge in dynamic range and high-ISO.
Now, do those things mean that the K-3 is the better choice? Not necessarily. $500 is a lot of money. $500 could be an additional lens. You'll have to decide for yourself if weather sealing and the other advantages of the Pentax camera justify the higher cost.
I think it is clear that the K-3 is the better overall camera. In fact, the K-3 and the D5300 are in two different classes and aimed at two different groups of people. The K-3 and the D7100 can be more directly compared. But sometimes a lesser camera has better overall value. In the case of the K-3 and D5300, the Nikon DSLR might actually be a better value, depending on exactly how you use it.