There's no consensus. Watch what looks best to you, not what the calibrator says. I think most users use auto1. The consensus is that Sony's auto-iris is the amongst the best out there. So try it. If nothing bothers you, there's not much downside. I think the main criticism is that in a scene like a light at the end of a tunnel, the auto-iris will make that light dimmer (and the darks darker) than with manual (or no) iris.
If your lumens are too bright, you can use manual iris to reduce lumens. If you don't have enough lumens for your screen, I noticed that manual iris off is slightly brighter than auto iris. For a while, when I had a 1.0 gain screen, but wanted to use low lamp, I preferred low lamp with no iris over low lamp with auto iris. Last year I installed a Dalite high power (2.4) gain screen, from my viewing angle it's probably 1.6gain. Now I prefer low lamp, auto 1 iris, because darkening the blacks seems more important than brightening the whites.