I've owned both and I would choose the SQ-A just about every time. The SQ-A is better built, more reliable, and can work without batteries (at 1/500 only, but hey, that's better than nothing).
Batteries and the battery compartment are a constant source of problems for the SQ-Ai. I could never get the four tiny batteries to fit properly into the compartment, so the darn thing only fired intermittently. The one big advantage that the SQ-Ai would have over the SQ-A, if you get a fully functioning camera, is that it is capable of TTL flash with the dedicated adapter and flash gun, which is very unique for medium format. The SQ-Ai also has a B mode, but this isn't really all that significant as all of the lenses, except the PS/B 80mm, offer T-exposures.