Which model of Blackberry did Robert Ney order for House of
Representatives? Which model and network works best in disaster
scenarios when telephones, cellphones and internet are down?

At the time of 911 attack, there was only one Black Berry out there.
It is produced by Research in Motion Ltd. in Ontario Canada.
US Congress is using it as a backup in case cell and phone lines r
down.
In truth, there is no "safest" solution.  Wireless PDAs (most of them
anyways)
tends to have their own network for just PDAs.  And the number
of user using the PDAs are relatively fewer than cells (much lower).
thus the chance of it clogging up is close to nill.  Also, most likely
terriorist won't try to attack the system because of the relatively
low social impact it will have (although with congress using it,
Blackberry network might be under attack in war situations).

http://www.pcworld.com/news/article/0,aid,65803,00.asp