I was hesitant about Mazaika because, well, MacOSaiX is free, but I downloaded the trial, experimented with it for about a week, and found myself impressed. Mazaika handled creating a library of 63,000 images without a hitch. And it renders mosaics very fast compared to MacOSaiX and MozoDojo, and with good color and tile adjustment.
I like that you can use multiple libraries in on image by selecting sections, rendering, switching libraries, selecting a different section, and so on.
It could have a more "Mac-like" look to it, but apparently that is a work in progress. And the developer is helpful and quick to reply to questions - always a good sign. For me, the registration fee was money well spent.