If you're meaning the image on the card in the Index PDF, that was a
GW Chaplain model, painting in
GK colours.
That particular sculpt was a Warhammer New Store exclusive model, that you could get by completing a collector's card, or something like that.
As for what would I use today? I'd consider starting with this new
Chaplain in Terminator Armour model,
or start with a standard
GK Terminator model and convert the Crozius.
I haven't seen the new Chaplain side-by-side with the current
GK Terminators, but I
suspect he might look a bit big stood next to them.