My Vet
DA Gunslingers before I started painting them (still a work in progress).
It's a stupidly expensive unit, but it pretty much wrecks everything. I typically drop the meltagun guy, and add a Librarian with Divination and a drop pod. Yeah, the turn it drops you don't get the warp charge for the Libby, but on subsequent turns... Wow.
I've been toying around with the idea of a Land Raider or Land Raider Crusader as a transport, but talk about all your eggs in one basket...
Make no mistake, this is a "fun" unit. You take it for the looks and sheer pleasure of using a rule called 'Gunslinger', not for its table top effectiveness.