I've been playing with both and from my observations the Sensis version still has more terrain and other details. For example park areas in green, pathways marked etc, also unlike Here the dual carriageway local roads are also shown as dual roads so easier to identify and get your mind around complex intersections.

I much prefer the look of Sensis to the Here version however there is some functionality in Street Pilot that is only compatible with the Here version, for example around highway mode and/or exit services that I noticed does not work with Senis.

Otherwise the general road detail & currency still seems to vary on both depending on the area.