The first point to be understood is that of steering. There are two basic types of steering, USS and OSS. USS stands for Under Seat Steering. While a bit more difficult to learn to steer, the USS styles are generally considered more comfortable on the upper body. One of the disadvantages, however, is that this type of recumbent is much wider than the OSS models, and is also difficult to steer when walking the bike.
The OSS, or Over Seat Steering bikes (aka ASS, or Above Seat Steering) are easier to learn and usually are much faster to drive. The OSS models are also much easier to steer when walking, though the shifting is rather slow performing and often requires more upkeep.
No recumbent bicycle reviews would be without mention of low and high racers. The low racer is a model type of recumbent which is built low to the ground. This is ideal for those seeking speed in their biking. This is the style that professional racers utilize. However, on city streets the low racers are less visible, thus a greater possibility for being hit by motorists exists (as well as a perpetual fear of this happening). Many bike enthusiasts find the low racers awkward to adjust to riding.
High racers are also quite fast, as many recumbent bicycle reviews will attest to. These too can become difficult to adjust to, particularly due to the incline of the seat. However, a characteristic that makes up for this, in many circles, at least, is the increased height, compared to the low models. The high racers are equivalent in height to normal street bikes, allowing for increased sight both for the rider and of the rider for motorists and other bicyclists.