Met with some American colleagues. Nice people but very different from the Brits I'm used to.
How were they different? 
They are very open and forthcoming, in a professional way. A Brit will--maybe--talk about the weather when forced to, and offer an awkward hello until spoken to again. The Brits know irony, though, and puns, and weird references to obscure things.
If you have to talk to someone entirely new to you, an American will probably be a better choice. If you manage to get past the introductions and the unspoken codes, a Brit is probably funnier.
