There have been a large number of improvements in pump technology and efficiency over the last few years visit your local bike shop for help in selecting the right one for your needs.
Types of pumps
Mini-pumps: These are the most popular pumps because they're lightweight and you can fit them in a bike bag. Many also mount on your bike frame. But you'll need to consider the extra hardware necessary for mounting them, and they take much more time to inflate a tire than does a large pump.
Frame pumps: These pumps squeeze-fit or attach onto your frame, either under the top tube or against the seat tube. They have a large capacity and will fill your tire in relatively few strokes. However, they are often heavier than mini-pumps and could be in the way when you're hoisting your bike to cross a stream or step over a boulder.
Floor pumps: These are perfect for home and can be used for many applications other than filling your bicycle tires. High-volume pumping lets you quickly fill your tires to a high pressure. It's a good idea to have a floor pump in addition to whatever kind of pump you choose to take on your bike, so that you can pump up your tires before each ride.
Built for road or trail riding
Road: Perhaps the most important factor in a pump for bike touring or racing is that it be lightweight.
Mountain: On the trail, you'll be more concerned with durability. Branches, flying rocks and the ground all have ways of banging into your pump. Choose a pump designed to handle the rigors of the trail. If you often find yourself carrying your bike across unrideable terrain, choose a mounting system that keeps the pump out of the way.
Another factor to consider if you race either on road or trail is speed of inflation. You don't want to lose valuable time pumping your tires when you should be pumping the pedals.
Stroke force and maximum psi output
If you're riding on trails, you don't need any more pressure than 55 pounds per square inch (psi). But if you're on a top-flight road bike, you'll need your pump to deliver as much as 120 psi.
Getting a pressure reading: gauges
Having a built-in gauge on your pump lets you monitor pressure to stay in the safety range for both your tire and your pump. It's also convenient because it eliminates the pump-and-test routine, shortening inflation time and reducing wear on your valve stem and pump connection and it reduces arm fatigue.
Taking care of your pump
Keep it clean! Dirt, sand and other grit can damage the gasket and scratch the inner chamber, making your pump stick and allowing pressure to escape before it gets to your tire. Periodically dismantle, clean and oil your pump to keep it working smoothly. Many bike shops and catalogs offer parts kits for most pumps. Kits are sold separately, and each includes O-rings, a head cap and a valve adapter. When using your pump, preserve the gaskets by making sure you have a tight seal on the valve stem and by avoiding pushing the pump past its pressure capacity.
Presta vs. Schraeder valves
In general, you'll most often find Schraeder valves (similar to those found on automobiles) on lower-priced heavy-duty or all-terrain mountain bike tires; bikes, for example, that sell for under $500. Presta valves are typically used for lightweight road bike tires and some mountain bike tires.
Identify which type of valve you have so you can adjust the pump to match. Most pumps manufactured today work on both types of valves. Reversible connections are fairly simple ask any shop sales specialist to demonstrate the adapter mechanisms.