Units to put a newb in charge of

First time i played 40k was at a GW shop in like 1996. They put me in charge of a dark angel drednought with lascannons and a missile launcher, and a techmarine hiding behind it.

I was wondering if some kid walked up to a game in progress what would be the best units to have them control.

I've got a tau army, and I'm scratching my head as to a simple unit that a first time player could control and have tons of fun with.

What about the other races?

A Space Marine Tactical Squad is the obvious answer I think, you can use them show how infantry moves and squad coherency and stuff. Covers a lot of basics, maybe a Combat Squad with a Sergeant (Chainsword Bolt Pistol) and a Flamer? Its a classic.

I think a key with newcomers is not swamping them with stuff though, so ignore some rules break tests, And They Shall Know No Fear and Chapter Tactics until later on.