HSI chips are pretty readily available (through the classifieds) in a mint state, whereas alot of the HSC chips that I've seen for sale are pretty well used, especially the low demons like 1s and 5s (not to say that mint ones don't exist, as they definitely do, they just don't come to market as often). The HSI chips also came to the community more recently, so there are significantly more being actively sold on the classifieds, which is opportunity for you to get some of the rarer denominations and fill in your set. I'm not sure about the quantities of the HSC chips, but the HSI sale was huge, and you can still find some of the chips like mint 1s that were originally available in massive quantity below or around $1 per chip in the classifieds. And personally, I think the HSI chips are just more attractive over all.