A scuba diving computer can be a divers best friend. It will allow you to stay down longer than if you were diving off of tables. There are many types and/or styles of dive computers you can choose from. Which one is best is really personal preference and is suited to the way you dive. The following are some of the choices you will have when purchasing your dive computer.
Console Dive Computer
A console dive computer is attached to the rest of the equipment via a hose. The console dive computers typically come with a pressure gauge. The readouts are typically larger than on a wrist dive computer so they can also be easier on the eyes.
There are also options for a scuba dive computer to be mounted on your hose (this is the type we currently use) or clip onto your BC. Choose whichever is more comfortable for you and fits into your price range.
Wrist Dive Computer
The wrist dive computer is very popular. These types of computers look like large watches and are worn on the wrist. They will tell you all you need to know at a glance. Some wrist dive computers are also able to be mounted in a console.
Sometimes the faces may be a bit small for all the information the computer can display, so make sure you will be able to read it underwater.
Unless they are air integrated and wireless (see below) wrist dive computers usually do not come with a pressure gauge. One small disadvantage here is that these can be pretty easy to misplace/lose.
Air Integrated Dive Computer
Air integrated dive computers are becoming more commonplace. An air integrated computer measures the tank pressure and then calculates how much more time you have left at the current rate of air consumption. The air integrated dive computer will tell you how much time you can spend at any exertion level.
An air integrated computer replaces the need for a submersible pressure gauge (SPG). One downside of an air integrated computer is that if it fails, you lose information on how much air you have left in your tank. Dive over.
Nitrox Dive Computer
With nitrox diving becoming more and more common, so are computers that are nitrox compatible. Even if you aren't diving with nitrox now, if you are even thinking of diving with nitrox in the future, it is probably worth it to purchase a nitrox dive computer. This will save you the expense of buying a whole new computer in the future. However, if don't think you will ever dive with nitrox, then there is no reason to pay for this feature. A standard air computer is probably $100+ less than its nitrox counterpart.
Hoseless Dive Computer
The hoseless dive computer consists of the receiver (typically worn on the wrist or mounted on the BC) and a transmitor. The transmitor attaches to the high pressure port of the regulator first stage and then sends your air information, wirelessly, to the receiver. The receiver looks the same as normal dive computers.
This setup cuts down on the number of hoses you need. There are now even hoseless dive computers that can accept signal from multiple transmitors - so you can even keep an eye on your buddies air consumption. Of course, this capability is really for the more advanced technical divers who may use different tanks on one dive. And, of course, we are talking some pretty high price tags here.
So just think about how you dive and what capabilities you need. The right dive computer for one person can be completely wrong for another person. Choose one that you are comfortable with and one that is right for you wallet.