4WD Bullbars fullfil a number of rolls for your four wheel drive. Their primary purpose of course is for vehicle protection, to minimise damage when colliding with animals that may unexpectedly cross roads, or for deflecting branches and vegetation when driving tight bush tracks. Other purposes include acting as a mounting point for spotlights, aerials and winches, to improve the approach angle of the front on the vehicle, and to some degree improving the general look of the vehicle. There are many variations of bar that can serve any or all of these requirements including steel bullbars, alloy bullbars, no-hoop bars, and nudge bars.
Steel Bullbars
Full steel bullbars will give maximum protection. They are very strong, as both a mounting point and for collision protection. They can also be colour coded to match your vehicle and improve the aesthetics. Depending on your needs this might be the only choice worth considering. The big downside is the weight which could typically be around 80kg plus lights and winch weights if you also add these. With a lot of extra weight hanging off the front of the vehicle there can be an effect on front suspension, steering, stopping and handling. This can be solved with suspension upgrades but you need to factor this in as well. Fuel consumption can increase both because of air flow drag as well as the extra weight. Another big downside is that the weight will eat into your vehicles rated payload capacity reducing how much other gear you can carry while staying legal. But if you are doing a lot of high speed driving on outback roads particularly at dusk or early morning when animals are often on the road the negatives will not be as important as the benefits to you and your safety.
Alloy Bullbars
Alloy Bullbars can look much the same as steel but are significantly lighter at typically half the weight. They generally come in polished silver but can also sometimes come as powder-coated black. They are not as strong as steel but can be a very good compromise depending on your usage. They also have the advantage of being rustproof. For tougher applications like winching, a steel bullbar is going to be better, but for general basic protection alloy ticks a lot of boxes without the weight drawbacks of steel.
Nudge Bars
4WD nudge bars are a popular option when accessory mounting is the primary requirement. Although nudge bars give very lttle additional protection, except perhaps a small amount of extra radiator coverage, they will provide a suitable mounting point for driving lights or antennas with minimal cost and very little negative effect on weight or airflow drag. They are also a significantly cheaper option, while still enhancing your vehicle's appearance.
No Hoop Bullbars
A newer option that is gaining popularity is the no-hoop, or no-loop bullbar. This is basically a steel bullbar without the upper loop sections. They can sometimes also include a small nudge bar style loop. This style of bullbar gives maximum protection to the bumper bar and below and has all the advantages of the full steel bar except for collission strike protection above the bar. They provide a small weight saving and can often greatly enhance the look of the vehicle.