Do they travel a lot?
-Keep in mind that many systems around the country are going APCO-25 digital, so that might be something to play in your decision. If you just stay around here, I think it will be a while until we see (non-encrypted) P25 being used regularly by Norman or Edmond or the State Smartzone system.
Would a handheld be better than a base for them?
-I like a handheld to take to events and work and malls and such, but a mobile is generally easier to read and use (bigger buttons and display!).
Do you have a brand preference?
-Radio Shack stuff is easy to buy (stores are close). I usually prefer Uniden because of features and options (most of which most people don't really need (like 5,000+ channels)).
There are lots of things to think about when purchasing a scanner. If you have the money to upgrade later, try something small, cheap, and easy to use. Hopefully, this will not discourage the user because of complicated programming or too many features/options. Trunking is pretty much required if you want to listen to much - that is ususally the thing people get confused about the most.
Good luck in a purchase, and let us know what you decide!