I've gone undetected on the surface in the visual circle and in the asdic/hydrophone circles while submerged. I'd bet it depends on conditions auch as weather, speed of your sub, depth, etc.
Now radar, I've had no luck. Last couple patrols off the US coast, I've run into US destroyers with radar that picked me up as soon as I entered the radar circle.

Fortuneately, the US destroyers at this stage are not very good.