Here’s what fits in each:
The medium size is actually not a big bag at all, and because it’s slim, it feels like the perfect size, actually. And it fits a lot. I think it will be more of a pleasure to use.
The mini is crazy-small. It only fits my phone and card case (which I use for keys, license, and a few cards). And seriously, with only those two things, it’s a squeeze. I think one of the iPhone plus phones wouldn’t even fit at all, but I don’t have one, so I’m not sure!