You don't buy an instant camera because you care about photo quality. You buy it because you yearn for a simpler, easier time, when photographs were tangible objects, and cameras came in cutesy colours and swallowed film.
Fujifilm's Instax Mini 70 is the newest addition to the existing Instax cameras. It adds such modern and exciting features as automatic exposure control (!!!), and a selfie mirror for better framing of selfies. There's also three different colours: white, yellow and blue, a major departure from the grown-up leather-and-metal look of the Instax Mini 90.
Otherwise, the 70 takes the same credit-card-sized Instax Mini film, costing about a dollar a shot. The camera itself is cheaper than the the Mini 90, though. Local prices aren't available yet but the 90 converts to about $285, whereas the 70 is closer to $200. That's still a little more than the Mini 50, but for the extra money you're getting a bunch more functionality, and a design that doesn't look like a third-grader's first camera project.