Keep in mind not all blades are created equal. Depending the razor you'll discover just how unequal they are. The irritation factor is going to be more so due to technique than blade edge when dealing with either extreme of a overly mild or aggressive razor. Mild it will be between sharp edge vs not so sharp edge, i.e. something like Feather blades vs everything else. To mild you'll be jabbing that razor into your face with a lot of pressure but very little cutting edge hitting the face, no irritation but no close shave either except with a super sharp edge like a Feather blade. The other extreme of aggressive every blade will be a face burner with very little pressure. With that said blade edges work about the same in a razor somewhere in the middle using sufficient pressure but not overdoing it.
With that said the most irritation free blade I've used would be a Ladas stainless steel blade. It is not my regular use blade but I've used in a cross section of razors and it was always smooth no matter how aggressive the razor, didn't cut as close as Bic Chrome Platinum which is my go to blade but it was consistent in it's smoothness just like a Bic is consistent in it's sharpness from shave to shave until it isn't.
With that said the most irritation free blade I've used would be a Ladas stainless steel blade. It is not my regular use blade but I've used in a cross section of razors and it was always smooth no matter how aggressive the razor, didn't cut as close as Bic Chrome Platinum which is my go to blade but it was consistent in it's smoothness just like a Bic is consistent in it's sharpness from shave to shave until it isn't.