I'd consider more than just speed. Size of HD and amount of RAM are also important.

>The other user's former laptop (OUFL) is not trustworthy, you can't use that.
>
>Whichever is the faster machine, use that. If it's the other user's, wipe it and start from scratch. If it's yours, start from scratch with the new disk.
>
>If your boss complains about wiping OUFL, tell him/her it's standard practice in most corporate environments.