If being close to the water taxi terminal is important, check out Isabel's Guesthouse. It's about a one minute walk from the water taxi terminal; you can see the terminal from the guesthouse. It's safe & clean. Here's a link to the Toucan Trail for more info...
http://www.toucantrail.com/Isabels-Guest-House.htmlAlso owned by the same family is Three Sisters Guesthouse, about a 3 minute walk from the water taxi terminal. You can find info on the Toucan Trail.
Both are situated in the downtown area of the City, and I wouldn't advise walking around alone at night there, so ask at the guesthouse for places to eat and take a taxi. Nerie's is a good Belizean restaurant nearby.
Get a taxi from the airport. Before exiting the airport terminal, try to find another person to share the taxi.
Here's a site I set up with some travel info...
http://belizebus.wordpress.com