There is a variety of bike pumps available on the market and it can be quite confusing to know which one you should get. However, there is certain rules that can help you make your choice. As your main pump, you should choose a good quality floor standing bike pump with ideally a pressure gauge to help you reach the correct tyre pressure without too much effort. Mini cycle pumps and CO2 Inflators are really useful for when you are out riding as their design is compact and lightweight to allow you to carry it in your jersey's pockets or in your bike bag.
The other thing you should consider when buying a bike pump is the type of valve your bike uses. As a general rule, if you are on a mountain bike, you will need a pump with a Schraeder head as it is most likely your tyre is fitted with a Shraeder valve. If you are cycling a road bike, chances are you have a Presta valve on your tyre and then need a pump with a Presta head. That said most pumps come with interchangeable heads and some valve adapters are also available.