This is a pretty tuff comparison because they're so close.
I prefer the machining and finish a little bit better on the Microfires. The cuts are sharper and the finish is smoother making it hard to hide imperfections. The Microfire's seem to have a slightly more reflective orange peel reflectors whereas the Boxer's texture is more frosty. If everything else is equal the Mircrofire should throw a little bit farther. There is also the issue of the reflector lottery with the Mircrofire with three unique styles that have been noted, Frosty OP, Shiny OP and Relative smooth. It's not truly "smooth" it's just been finely machined and then had the reflective coating applied. Up close or with a magnifying you can see that it slightly rough yet much smoother than the other two options. This difference is mainly noted among the K3500 which will out throw either 24W light. Here is a poor quality picture of mine but you can still see the machining markes:
I don't mind that it's not super smooth because the spill light is more blended and useful for more tasks.
There were more initial problems associated with the Microfire lights than the Boxer at its release. Last time I spoke to Mike at PTS the Boxer had a return rate of 2 per 100 but it's probably even less than that now. If I remember correctly there were many more Microfire failures and that's why I went with the Boxer24 at the time.
I've since sold the Boxer but it was a very nice light. I currently own the K3500 and it's also very nice. My use time with the K3500 has long surpassed the time that I ran the Boxer and it's still going strong on the original battery. My personal feeling, from ownership and info from other K3500 owners is that Microfire has probably closed the quality gap to Wolf-Eyes some over the past 8 months.
I think either light is good in the 24w class but the Boxer uses conventional 168 / 18650 batteries which is a nice feature. The Boxer also doesn't have holes going around the head and will probably stay more clean.
If you need outright throw and performance the K3500 will out perform the 24W lights at the sacrifice of length and a little more weight. If that's not a big deal to you, possibly consider it. I get a lot of use from mine.
I can't comment on color temperature for the K2000 but the Boxer24W seems ever so slightly warmer than the very blue K3500. From looking at past pictures, the K2000 and Boxer24W appear to have the same bulb but I'm not positive if that's really the case.
In short, get the one that appeals to you the most or is the best price. The lights are close to equal in my experience.