What's the safest shape for homemade hard-candy I'm thinking about trying to make some wintergreen hard-candies out of gum paste + wintergreen extract, but wasn't sure what shape / size to make them.

It got me thinking, "What shape should these candies be so that it's less likely that someone might choke / otherwise hurt themselves while eating them?" 

I feel like a perfect sphere is probably the most likely to be accidentally swallowed, but hard / sharp edges may not be good for the inside of your mouth. Tried looking this up online, but didn't really get worthwhile search results-- beyond hard-candies being the most likely food item for a child to choke on.
Spherical or spheroidal foods are indeed the most likely to be implicated in choking - grapes are well known. But you're unlikely to get sufficient statistics to answer fully. Most of the medical literature I've seen is at least as concerned with size, and of course that changes as you eat the sweet. You'd have to start unusually small for size to be much help. 

Hard edges are much less of a concern. You'd struggle to get them sharp enough to do any actual damage, and the corners dissolve fastest, meaning they blunt almost immediately. This also means that the corners of something like a cube will go fairly fast, and you'll be left with a near-spherical blob.

You might be best off with something like a coin shape - a flattish disc or oval. This is a traditional shape for barley sugars, and I've also had hard fruit sweets that shape. While coins do show up in the choking statistics, they're very common items for children to investigate, including by taste and when not supervised.