What size engine should you get in a motorcycle?

Many factors affect choice of engine size. Of prime importance is the licence you hold and any restriction to engine size that it carries. After that it is what you want the bike for and the type of bike that best suits the purpose. Then it is what bike in that group fits you best, regardless of engine size. The best bike is the one you are part of not the one you perch on. Finally, engine and performance depend on what you want to do, the type of riding you intend to do, your weight, your passenger/gear weight. Then the engine itself; Japanese multi cylinder engines need high revs to produce power and a 'good size ' for general use is about 600cc and is probably the most economical in terms of servicing, fuel economy, insurance etc. Twins and singles (excluding Ducati and Vrod) are lower revving but have a lot more torque for pulling up hills and carrying weight but generally less acceleration and a lower top speed.