Verdict
A1 Mini is the modern speed pick (300mm/s, AMS Lite compatible, 180mm cube). Prusa Mini+ is the venerable workhorse (180×180×180, lower failure rate at 2-3%, no multi-color option natively). The A1 Mini is faster and cheaper; the Mini+ is more reliable per print.
Buy the A1 Mini if: speed matters, multi-color is on the roadmap, budget is tight.
Buy the Mini+ if: reliability matters most, you already use other Prusa machines, you don't need multi-color.