Apples and oranges. Both have their challenges and rewards.
Koto gives me the chance to work on stuff in a format more like the old model kits I used to build (sanding and puttying parts, painting, and assembling which I always enjoyed), and I have some freedom to paint them how I like within the bounds of the character design. That, and I am able to show it off within a week or two of finishing it. The only downside is that I am not a huge comic fan and don't collect statues, especially comic related stuff (cause I tend to be a completist and there's just too much of it), so the stuff I do for them isn't stuff I collect. I'm proud to be part of making cool pieces like that though.
Erick and I will be doing stuff for Yamato though, and fantasy females are something I will collect. Same format as Koto work, but different subject matter.
When painting for Sideshow, I was mostly just doing parts of a given piece, so I was rarely able to see the finised product until it was finally revealed. The upside was that I got to be part of making the figures I myself really wanted and that have a huge fan base, ie, Boba Fett, the upcoming Darth Vader, Jason PF, etc. The biggest downside being that it's sometimes quite a while between paint and reveal and then again to final product release. Like, Boba Fett is due out at the end of this month, just about a year to the day that I actually painted the parts for it. And there's stuff I painted over a year ago that still haven't been revealed, though I think we'll see some of it at SDCC this year.