The three "major hotels" in Belize City are The Princess Hotel & Casino, the Radisson and The Great House. All three have their issues, but any one of them would do for a one night stay.
The Princess is probably the biggest and is a bit away from the other two, which are located in the Ft George area of town. The best thing about the Princess is the location if you're coming or going from the marina, as it's right out the hotel's back door. If you're looking for convenience to the marina above all else, the Princess wins hands down.
The biggest drawback, in my opinion, is the place is kind of sleazy. I've only passed through it, i.e., used the restroom facilities while waiting on the car transfer after arriving by boat, but I wouldn't want to stay there. The hotel had kind of a creepy cheap-glitzy vibe; maybe it was the casino.
The Radisson in Belize City isn't up to par with the Radissons in the US but it's a better choice than the Princess in terms of the accomodations. It's about five minutes from the Princess and its marina by cab. Unlike The Great House, the Radisson has a pool and elevators. The Radisson's not as nice looking in real life as it is in the pictures on its website, but it's where I would stay if it weren't for The Great House.
The Great House is somewhat long on third world colonial charm but very short on services beyond the basics of a place to stay. Despite the title in Gaz's link above, there is nothing luxurious about it. Located right across the street from the Radisson, it's a former family residence converted some years ago into a hotel. The ground floor is an open entryway with shops running down the sides that leads into the hotel's outdoor restaurant, The Smoky Mermaid. The tropical garden setting is very nice, and while the food's ok I recommend you keep it simple to improve your chances.
The hotel lobby is on the second floor, and the rooms are on both the second and third floors. Since there's no elevator and very little staff, be prepared to haul your luggage up and down the stairs yourself unless you get lucky and a young man happens to be hanging out who will do it for you in exchange for a tip. He was there when we checked in last time but had already gone to lunch when we were ready to check out.
The rooms are nice enough with the basic furnishings and come in a variety of shapes and sizes. Our tv didn't work, but we were there for only one night and didn't care. Checkout's by noon sharp, so if your transfer's coming later then be prepared to hang out in the first floor's entryway, which thankfully has some comfortable seating.
The Radisson and Great House share 24 hour security services, so they're safe enough but don't wander off the properties at night under any circumstance and be extremely careful if you choose to go out even during the day.
My wife and I will be there for three nights, 7/28 through 7/30, before moving on to Turneffe Island Resort on 7/31. Maybe we'll see you there.