There are lots of things to consider when you decide to buy an Rc boat for the first time. First and foremost, you'll have to decide whether to go with Nitro or Electric. While a whole article can be done on this subject alone, the long and short of it is, Electric is a bit slower with less runtime, but easier to maintain, cleaner, not as loud, and much easier to run and keep running. While nitro is faster, has longer run times, but stall often. Even seasoned Rc boat racers have a hard time keeping them running. And they are also being restricted from use in lots of places because of high noise.
            Next is water conditions. Are you running in wavy conditions or a protected area with flat water?
            After that comes size of the area you plan on running. Sure everybody wants an 80mph boat, but if your running on a small pond it may be useless and cause problems because running at 1/2 throttle can harm some motors, engines and ESC.
            Next you'll also need to consider whether some day you may compete in organized racing. You may want to contact a local club to see what type of hulls they are running. You don't want to put a ton of money and effort into a hull only to find out when you want to race there are no other boats in that class.

 "Mono" Hulls
There are two types of Mono hulls the "Deep Vee" and the "Shallow Vee". They look similar but are very differently.
 

          The Deep Vee design handles ruff & choppy  water better then any of the other fast electric hull designs. They also turn great in both directions & are  easy to setup. This make this type of hull perfect for the beginner.
          Due to the large amount of the hull that rides in the water causing drag, these are also the slowest of all the FE hulls. Very fast Deep Vees will run with most of the hull out of the water, this is great for speed but can cause erratic handling. The Yellow OffshoreElectrics Titan40 is a Traditional Deep Vee hull. The below picture shows the transom angle which helps it cut through the waves.

          The Shallow Vee has a much flatter bottom which when at full speed has less of the hull touch the water. This make the Shallow Vee faster. But the Shallow Vees tend to slide around corners, instead of carving the turn. Below is a picture of a transom with much less angle.

Catamarans         

           The catamaran design is a cross between a hydro and a deep vee. With the center tunnel, the hull has less drag then a deep vee, while also creating lift. The twin hull design makes it both faster then a deep vee, with the added benefit of better ruff water capabilities then a Hydro. The only draw back to the design is that a blow over in windy conditions is possible.  They are somewhat harder to setup then a deep vee. At very high speeds the cat will be more stable then the mono because of the twin hulls.
 

Outboard Tunnels
 

          Although it sports a twin style hull similar to a catamaran, that's where the similarities stop. Because of the low profile of the freeboard (hull sides), this boat will not take the waves very well. While faster then a traditional offshore catamaran its made for flat water only. Why Kyosho named the pictured boat a "Wave Master" we're still trying to figure out?
 

Scale Hydros
 

          The Scale Hydro is the fastest of all the scale hulls. The only hull design faster is a rigger which doesn't resemble any full scale boats. A well designed, balanced and powered Hydro will run with only a very small part of each sponson touching the water, while the transom will be lifted out of the water by prop. Because of this, the  hull has very little drag.
          They are hard to setup correctly. And most are designed to make right turns better the left turns.  Most need very flat water to run. Windy conditions easily cause blow overs and choppy water will cause the nose to stuff the waves.
 

 
Pictures courtesy of Doug of Madison Rcboats.org

Pictures courtesy of by Nate West!

Riggers
 

          If you want to run the fastest you can on flat water , there is no substitute for a Rigger! With straightaway speeds faster then any of the other hull designs, along with razor sharp handling makes this, the hull to beat in racing. Set up is the hardest of all the hulls, with the exception of the canard style hull. As you can see in the left picture, on a well setup rigger not much touches the water! One of the downfalls to the rigger style of hull is that they like to run at full speed. The picture on the right is a rigger at low speed, but once on plane they practically fly!

Picture courtesy of Gregor Vida

Picture courtesy of Bryan of
Conroe Fastelectrics.com

Canards
 

          A Canard looks like a backwards Rigger. While a well setup Canard is slower in the straights then a Rigger, it will have faster cornering speeds. This type of hull is only for the seasoned Rc boating enthusiast. Not many people are able to set these up successfully.