The factory bumper is just Aluminum Tube stock bolted to brackets at the frame rail ends, then the plastic bumper cover goes over it. The factory set-up is nice but is limited on approach angle (though factory angles are still nice) and very fragile when it comes to dragging on obstacles such as rocks and hard earth.
A full replacement bumper like a ShrockWorks, Demello, CBI, ect. are full replacement bumpers that offer a multitude of benefits.
+Increased Approach Angle
+Better Durability (i.e. scraping obstacles, dragging on things)
+Better front end protection (the washer bottle being one of the weak points depending on the brand, i.e SW has plates to cover the washer bottle where as Demellos typically do not)
+Solid mounting platform for accessories such as lights and winches
+Strong Recovery points due to being a direct extension of the frame
+More adaptable for body lifts (you can only do so much as the bumper skin connects at both the frame and the body and will start stretching and looking awkward)
+Better Tire clearance
-Cost
-Weight (Aluminum versions do exist, though I personally do not like Aluminum's "stickiness" on obstacles)
-More difficult installation (mainly due to the weight, usually helps to hav a second person help install it)
-Often requires supporting mods to negate weight (i.e. stronger springs & shocks and/or suspension lift kits)
-Appearance (some people don't like the heavy duty look, personally I love it)
A Hidden Winch like BB or CBI is a compromise between the strength of an aftermarket bumper and the appearance of a factory front end.
+Stronger than factory Aluminum bumper
+Typically built tough enough to stand up to a moderate front end collision
+Provides a stable platform for accessories (depending on the design, some can fit and entire winch, others are just receivers)
+Much more "stealth" looking option than a full metal bumper
+Typically cheaper than an after market bumper
+A little easier to install than an aftermarket bumper
+The winch is removable (depending on the design)
+Typically lighter & requires less supporting mods (i.e. springs & shocks)
-Does not address approach angle problems (many times I have noticed that the SW bumper has cleared inclines I would have ruined my factory front end on)
-Does not address wheel well issues that affect tire fitment (may require heavy trimming/reshaping fender wells depending on tires and how hard you wheel)
-Does not address durability issues with the factory bumper skin
-Factory recovery points can be iffy fro heavy off-road use (some members haven't had issues, others have damaged factory "tow points")
-The winch is removable (depending on the design)
It really depends on the type of vehicle you are building and your budget I guess? A hidden Winch/Receiver is probably not a bad idea for those of us who don't off-road hard in places where approach angles are going to be steeper and there's a very real risk of snagging your front end on obstacles. I don't see them as having to be either or deals, some vehicles are just not going to be driven as hard as others and so there's no reason to invest in a $1700 bumper if you're never going to fully utilize it.
