Most of the time, it's much of a muchness and you will need to ride a few designs to see what suits you. Some designs use a single pivot design. This means that as the rear triangle moves, it directly compresses the rear shock. The main benefit of this is simplicity. (I stand to be corrected?) Some use a single pivot with remotely activated shock. The benefits of this are less pedal bob (i.e. you want the rear triangle t move when the bike passes over a bump, not when you apply pressure downward on the pedals. The other designs are usually multi-pivot, and usually try and improve the activation of the shock. The ideal is a shock that doesn't lose power on uphills, handles small bumps smoothly, but can still soak up the huge knocks. At the end of the day, try out a couple of bikes, find one you like, learn about it's rear suspension design, and MOST IMPORTANTLY learn how to argue that your design is far superior to everything else in the market! This does become tricky when your expensive Santa Cruz shares a design with the value for money Raleigh, but you will have to find your own arguments for that
