I use both handstrap and neckstrap...
I will never shoot with a single camera. I guess that this is because I cut my photographic teeth with prime lenses and IMO a multiple camera system is the only efficient way to shoot with prime lenses. I think it is ridiculous to be switching lenses in the field in the middle of a shoot and also think that using one of those relatively slow-focusing, small aperture, mediocre IQ, zooms with the extensively wide focal range limits the capability of any photographer.
I want relatively instantaneous focus, a wide zoom range, decent apertures and, above all, top-notch IQ when I am shooting. My lens duo of choice is the 17-55mm f/2.8 IS and 70-200mm f/4L IS lenses on two bodies. I am willing to pay the price in extra weight. There is no real problem regarding extra cost. I use a 30D and a 350D in this system - the two cameras are worth less than a 40D.
I will always have these two lenses on dedicated cameras and will carry the camera with the 17-55mm f/2.8 IS lens around my neck on an Optech Reporter Strap and will have the 70-200mm f/4L IS lens in a holster case at my left hip. I have a hand strap on the camera with the long lens and will not use an OEM hood with this lens because the OEM hood is far to big and bulky and restricts easy removal from the holster case for shooting. My wife has sewn Velcro tabs on the left shoulder of the vest and I can fit the Velcro belt tab of the holster over the waist adjustment strap of the vest. That way, the holster case doesn't swing around when I run. Speaking about running or climbing. I have an OPTECH Stabilizer Strap which fits around my chest that has a neoprene pad with a lens hole. Slipping this pad over my camera will secure it to my chest and not let it swing. It slows down the use of the camera a bit but, I will only use this type of security when I am doing manuevers which could cause the camera/lens to be damaged if it was not secured tightly to my chest.
Instead of the OEM hood, I use a round screw-in hood which is a LOT MORE COMPACT (the OEM hoods for the 70-200mm series lenses are designed for full frame cameras and are overkill with 1.6x format gear), will shade the lens equally if not better, will facilitate the use of a CPL and will protect the lens from impact damage as well (if not a heck of a lot better) than the OEM hood. As an example, I fell to the concrete one day while shooting with a 30D and an L lens around my neck. The screw-in hood took the impact of the fall and broke but, it saved the lens. I don't know if the OEM hood could have done as well - but, would certainly not have done any better. Instead of a Canon lens cap, I use an OPTECH Hood hat to protect my lens. It is easy and quick to remove and place in my pocket.
I will often shoot with other configurations with my several lenses depending upon the needs of the shooting day. I have replaced my Tamrac Holster Case with a Think Tank Holster Case because the Think Tank has a zipper extension which will accommodate a longer lens.
When I shoot with my 70-200mm f/4L IS lens and my 300mm f/4L IS lenses on two cameras; I will have the shorter lens around my neck on the strap and the longer lens in the case with hand strap.
If I have my 300mm or 400mm lenses on a tripod, I will hang the holster case from the hook at the bottom of the tripod center column. With the 70-200mm lens configured like I described above - it is easy to reach into the holster remove the camera/lens and start shooting hand held. Hanging the holster keeps me from holding the weight of the camera/lens when I am shooting with the tripod mounted camera/lens and also keeps the holster safe from being tripped over or ripped off by a thief.
It is very quick to flip open the holster, insert my hand into the hand-strap, withdraw the camera, rip off the Hood Hat and start shooting. It takes a heck of a lot less time to do it than it does to describe doing it. AND - it is one heck of a lot faster than trying to switch lenses in the field.
Here are links to my equipment:
Reporter Strap:
http://www.optechusa.com …UCT_SUB_ID=&CATEGORY_ID=4
U use this strap because I occasionally will carry a third camera and lens. Three cameras used to be my standard load before I got the 17-5mm f/2.8 IS and was able to cut down to two cameras and lenses most of the time.
Hood Hat:
http://www.optechusa.com …UCT_SUB_ID=&CATEGORY_ID=6
Think Tank Case:
http://www.thinktankphoto.com/ttp_product_DgtlHlstr.php
Hand strap:
http://cgi.ebay.com …ZWDVWQQrdZ1QQcmdZViewItem
I don't like the type of hand strap which secures to the wrist because it is not as fast to use when removing the camera from the holster.
Round screw-in hood:
http://cgi.ebay.com …ZWDVWQQrdZ1QQcmdZViewItem
Stabilizer:
http://www.optechusa.com …UCT_SUB_ID=&CATEGORY_ID=4