A3 is a great mag for neck humbuckers, very underappreciated. People hear it's light in the lows and mistakenly expect it to be thin. Instead it's vintage crisp, warm and sweet. My "Aha!" moment happened with a custom A3 neck pickup that James at Rewind made me a couple of years ago as a companion for his Pale Rider bridge pickup. Since then I'm a believer.
UA5 has been my go-to for a couple of bridge humbucker swaps too- perfect midpoint between A5 and A2. I have a couple of old Gibson Shaw humbuckers with stock UA5s, but if it weren't for this forum I probably would never even have heard of that mag.